thanks for the reply jrmunday
However my installation path is as follows " d:\vmware\vmware authentication proxy " unless the spaces might be an issue ?!?!? (or maybe length might be a problem). I was looking through the 5.1 upd 1 release notes and they didnt mention the "unknown error" issue so I assume that it is no longer relevant in 5.1up1. I've tried it without the spaces but still no joy - fails straight away. 
regards
Munster99