Java 6 43 32-bit
Still having the same issue...
Filemaker usually recommends a full re-install when inexplicable WPE errors occur:
1. Un-install FileMaker Server (stop services, drag database folders to the desktop, make sure that the FileMaker Server directory has been removed)
2. Un-install IIS
4. Re-install IIS
6. Re-install FileMaker Server
Unfortunately there is still not an error code reference specific to WPE that I know of, allthough -1 and 0 are usually fairly generic codes anyways, that cover numerous issues.