I'm getting an "Application Error" on a Paperwhite 1 (gen 5) running FW 5.4.4.2 when running the latest head code (0.6.6+).
It does look like it's a Java versioning issue.
140101:050315 cvm[15403]: java.lang.UnsupportedClassVersionError: com/github/chrox/kpvbooklet/KPVBooklet (Unsupported major.minor version 52.0)
140101:050145 system: I usbnet:kh_msg::waiting for volumd . . .
140101:050147 system: I usbnet:kh_msg::reconfiguring usb0 interface
140101:050147 system: I usbnet:kh_msg::starting telnetd
140101:050147 system: I usbnet:kh_msg::starting sshd
140101:050147 dropbear[15979]: Running in background
140101:050150 powerd[1078]: I lipc:evts:name=charging, origin=com.lab126.powerd:Event sent
140101:050150 lipc-send-event[15984]: I lipc:evts:name=usbPlugIn, origin=com.lab126.hal:Event sent
140101:050150 g_ether gadget: high speed config #1: CDC Ethernet (ECM)
140101:050155 dropbear[15987]: Child connection from 192.168.15.1:50500
140101:050155 dropbear[15987]: Pubkey auth succeeded for 'root' with key sha1!! 70:c9:51:2f:61:50:6f:8e:9e:e2:f2:e9:13:b1:28:69:35:0f:5d:38 from 192.168.15.1:50500
140101:050155 dropbear[15987]: User root executing login shell
140101:050203 todo[1072]: I todo:ProcessingToDo:status=starting,reason=NetworkStartup:Started processing ToDo
140101:050203 cvm[15403]: I lipc:evts:name=credentialsInstalled, origin=com.lab126.DeviceAuthenticationService:Event sent
140101:050203 todo[1072]: W url_builder:GetURLWarning:reason=missingGlobalParameter,param=currentCountry:
140101:050203 todo[1072]: E todo_get_document:GetToDoFailed:reason=ensureConnectionFailed,error=5:
140101:050203 todo[1072]: E todo:ProcessingToDoFailed:reason=getDocumentFailedNullDocument,errno=0:Null ToDo document returned
140101:050304 cvm[15403]: W IndexerThread:Warning::Indexer low heap slowdown 1
140101:050305 powerd[1078]: I def:battinfo:cap=97%, mAh=1090mAh, volt=4187mV, current=208mA, temp=71F, bp=4187mV, lmd=1126mAh, cycl=0, cyct=0:
140101:050306 powerd[1078]: I lipc:evts:name=battLevelChanged, origin=com.lab126.powerd, fparam=97:Event sent
140101:050315 Xorg: I GestureEngine:perfScenario::Sending button 1 down 1388581395.046766
140101:050315 powerd[1078]: I lipc:evts:name=t1TimerReset, origin=com.lab126.powerd:Event sent
140101:050315 cvm[15403]: I def:print::perfScenario CVM posting MouseEvent[MousePressed] time=1388581395098
140101:050315 cvm[15403]: I def:print::
140101:050315 root: perfScenario CVM received X11 ButtonPress button=1 time=1388581395.098611
140101:050315 Xorg: I GestureEngine:perfScenario::Sending button 1 up 1388581395.170289
140101:050315 root: perfScenario CVM received X11 ButtonRelease button=1 time=1388581395.202139
140101:050315 cvm[15403]: I def:print::perfScenario CVM POINTER_CLICKED-gen btn=1 -> radius=2.0 time=1388581395204
140101:050315 cvm[15403]: I def:print::
140101:050315 cvm[15403]: I def:print::perfScenario CVM posting MouseEvent[MouseRelease] time=1388581395204
140101:050315 cvm[15403]: I def:print::
140101:050315 cvm[15403]: I def:print::perfScenario CVM posting MouseEvent[MouseClicked] time=1388581395205
140101:050315 cvm[15403]: I def:print::
140101:050315 appmgrd[1081]: I appmgr_registry:app_found_for_uri:lipc_app_id=com.github.koreader.kpvbooklet,executable=NONE:
140101:050315 appmgrd[1081]: I appmgr_history:FOUND_APP:lipcId=com.github.koreader.kpvbooklet:
140101:050315 appmgrd[1081]: E lipc:dbuserr:name=org.freedesktop.DBus.Error.ServiceUnknown:Receive Dbus error message (DBUS_MESSAGE_TYPE_ERROR): The name com.github.koreader.kpvbooklet was not provided by any .service files
140101:050315 appmgrd[1081]: E appmgr_lipc:lipc_set_prop_fail:lipc_status=3,app=com.github.koreader.kpvbooklet,property=go:send app command
140101:050315 appmgrd[1081]: W appmgr_history:unable_to_send_go:lipc_id=com.github.koreader.kpvbooklet,LipcStatus=3:Unable to send GO, re-loading
140101:050315 cvm[15403]: I BookletManager:StartingBooklet:booklet=com.github.koreader.kpvbooklet:
140101:050315 appmgrd[1081]: I appmgr_history:app_state_change:lipc_id=com.github.koreader.kpvbooklet,state=EXECUTED:
140101:050315 cvm[15403]: E BookletManager:BookletClassInitError:class=/opt/amazon/ebook/booklet/KPVBooklet.jar:
140101:050315 cvm[15403]: java.lang.UnsupportedClassVersionError: com/github/chrox/kpvbooklet/KPVBooklet (Unsupported major.minor version 52.0)
140101:050315 cvm[15403]: at java.lang.ClassLoader.defineClass0(Native Method)
140101:050315 cvm[15403]: at java.lang.ClassLoader.defineClass(Compiled Method)(Unknown Source)
140101:050315 cvm[15403]: at java.security.SecureClassLoader.defineClass(Compiled Method)(Unknown Source)
140101:050315 cvm[15403]: at java.net.URLClassLoader.defineClass(Compiled Method)(Unknown Source)
140101:050315 cvm[15403]: at java.net.URLClassLoader.access$100(Compiled Method)(Unknown Source)
140101:050315 cvm[15403]: at java.net.URLClassLoader$1.run(Compiled Method)(Unknown Source)
140101:050315 cvm[15403]: at java.security.AccessController.doPrivileged(Compiled Method)(Unknown Source)
140101:050315 cvm[15403]: at java.net.URLClassLoader.findClass(Compiled Method)(Unknown Source)
140101:050315 cvm[15403]: at sun.misc.Launcher$AppClassLoader.findClass(Compiled Method)(Unknown Source)
140101:050315 cvm[15403]: at java.lang.ClassLoader.loadClass(Compiled Method)(Unknown Source)
140101:050315 cvm[15403]: at sun.misc.Launcher$AppClassLoader.loadClass(Compiled Method)(Unknown Source)
140101:050315 cvm[15403]: at java.lang.ClassLoader.loadClass(Compiled Method)(Unknown Source)
140101:050315 cvm[15403]: at java.lang.ClassLoader.loadClass(Compiled Method)(Unknown Source)
140101:050315 cvm[15403]: at com.amazon.kindle.restricted.booklet.impl.BookletManager.Tnb(aqc:827)
140101:050315 cvm[15403]: at com.amazon.kindle.restricted.booklet.impl.C.run(aqc:1537)
140101:050315 cvm[15403]: at com.amazon.ebook.util.b.a.run(ftf:252)
140101:050315 cvm[15403]: at java.lang.Thread.run(Unknown Source)
140101:050315 cvm[15403]: at java.lang.Thread.startup(Unknown Source)
140101:050315 appmgrd[1081]: I appmgr_lipc:set_appmgr_run_result:propName=runresult,buf=1:com.github.koreader.kpvbooklet:entry
140101:050315 appmgrd[1081]: I appmgr_history:app_state_change:lipc_id=com.github.koreader.kpvbooklet,state=REGISTERED:
140101:050315 cvm[15403]: I BookletManager:TerminatingBooklet:booklet=com.github.koreader.kpvbooklet:
140101:050315 pillow[15030]: I def:show-system-alert:id=appmgrAppFailedFatal, altId=appmgrAppFailedFatal, alertLogInfo=undefined:
140101:050315 appmgrd[1081]: E lipc:dbuserr:name=org.freedesktop.DBus.Error.ServiceUnknown:Receive Dbus error message (DBUS_MESSAGE_TYPE_ERROR): The name com.github.koreader.kpvbooklet was not provided by any .service files
140101:050315 appmgrd[1081]: E appmgr_lipc:lipc_set_prop_fail:lipc_status=3,app=com.github.koreader.kpvbooklet,property=load:send app command
140101:050315 appmgrd[1081]: I appmgr_lipc:default_alert_displayed:app_lipc_id=com.github.koreader.kpvbooklet:show_simple_alert
140101:050318 Xorg: I GestureEngine:perfScenario::Sending button 1 down 1388581398.303466
140101:050318 pillow[15030]: I def:button-press:target=simple_alert,button=1:
140101:050318 Xorg: I GestureEngine:perfScenario::Sending button 1 up 1388581398.458791
140101:050318 pillow[15030]: I def:button-release:target=simple_alert,button=1:
[root@kindle root]#