Visio SaveAs Displays "File not found"

[Yangyong]

We have a C# project, which uses Visio Drawing Control to draw diagrams. We
have a lot of clients who use the program happily without any problem. The
program gone through several updates. And suddenly, one client has this
problem. When they try to save visio file, they get the "File not found"
message.

The running environment is: Visio 2007 sp2, .net framework 3.5 sp1, windows
XP. And the client has used this software without any problem before update.

I injected a lot of log message, and identified problem as:
this.axDrawingControl1.Document.SaveAs(visioFileFullPath);

It's quite strange because only this client has this problem. We even copied
all the running folder from client and run it on our machine, and it runs
without any problem. We asked the client to upgrade to lastest Visio Service
pack, and .net framework service pack, disabled all the Visio add-ins,
macros. Nothing works.

Please help!!!