I ran into an issue with one of our repositories - every job in the particular repository was failing with the error:
An internal error occurred during execution, please contact Quest support if the error persists. Error Message: There is an error in XML document (823, 223).
This error is commonly caused by a corruption or issue with the manifest file as detailed here.
To fix it, go into the manifest file for the repository (GlobalManifest.metadata), make sure that all trailing brackets are closed, and add </vRangerGlobalManifestFile> at the end of the document.
Save and test.