Some time ago I wrote an article regarding new methods in Domino 8.5.2 release: NotesAgent.runWithDocumentContext(doc) behaviour .
At those days I found a cryptic error:
Exception occurred calling method NotesAgent.runWithDocumentContext(lotus.domino.local.Document) null
when trying to execute, from SSJS code, Notes Agents that had the option "Run as web user" unchecked.
In Domino 8.5.3 you still get the error if the option is unchecked, but you get and extra error message I don't remember having seen in that release.
HTTP JVM: CLFAD0134E: Exception processing XPage request
Googling, you can find that these error can be caused by other reasons, but the one described above could be one of them.