Thisworkbook.path empty or starts with backslash
 

I have a spreadsheet for clients that contains a VBA procedure that
refers to thisworkbook.path. One client cannot get this spreadsheet
to work on his new PC. We have been able to determine that on his
computer thisworkbook.path returns either nothing (totally blank) or
something that looks like a network path (starts with "\"). Note that
this file is, when sent to him, read only. I also sent him a test
file that wasn't read only. He saved it onto his C: drive and opened
it, and it showed that thisworkbook.path was blank. Resaving the file
from within excel and re-running the test returned the actual
thisworkbook.path, which is C:\program files\Foo\

Does anyone have any ideas why thisworkbook.path isn't working in this
case? Thanks for any help.