"Error 1324 Error starting AutoCAD 2015

I'm currently trying to start ACAD 2015 on a Windows 7 machine and it's throwing up a "Error 1324 Error. The folder path 'My Documents' contains an invalid character." whenstarting AutoCAD 2015

While the path is mapped to a UNC drive, we've tried mapping the drive via the settings here: http://upandready.typepad.com/up_and_ready/2011/10/autocad-family-1324-error.html

We've also tried right clicking on the "My Documents" folder and changing the path to a mapped drive.  

I know this has come up before, but none of the usual solutions seem to work.  

Has anyone seen this and resolved it a way that's been overlooked? 

Thanks in advance! 

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