In trying to debug, I output the value of schemaBaseURI and get a well-qualified file (directory) name. The error, however, implies that only the validator is failing when it detects the drive letter C .
Curious, this may be a limitation with this and using Windows. This could be a total blocker here. Looks like the library does not like the Windows path.
This logic is coming from the workflow logic that was introduced in 10.29. Would you be able to try with the latest 10.28 version instead (this is currently 10.28.48).