A change was made in v6.2a, intended to improve the error reporting when running script code, that we just discovered can have actually the opposite effect (at least for VBScript syntax errors), and it's possible that this change also results in the sporadic error you mention here (if so, due to a bug in the ActiveX script host or VBScript script engine).
The
main download has been updated with a patch that backs out the problematic change to correct the
'Unknown error' rather than detailed error information when invalid VBScript code is executed inside VBP, and may also help with the sporadic error you reported here.