Problem with session data on PHP4/Win2k

Sorry for the cross-post, but no one at DevShed seemed to have an answer... I'm getting the following error in a script that makes use of sessions: "Warning: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (C:\PHP\sessiondata) in Unknown on line 0" I'm using PHP4.0.6 on Win2k with IIS 5.0. I've already checked the permissions on c:\php\sessiondata, and everything should be ok. The script has the same problem on my web host's server. It does *not* have this problem on my desktop machine (MacOS X/Apache/PHP4.0.6). Here's the strange part: I've noticed that I can go into that directory and actually see the session files. When I open them, I can see the first value set by the script. None of the others seem to make it into the file. But it seems odd that it's writing some session data, and then telling me it can' t write the session data. Could there be something wrong with the code that I'm missing? As I said, it works fine on Darwin/Apache. But a bug in my code would explain why it doesn't work on two different machines. But then why would it work on MacOS X? Very confusing. Anybody have any ideas? Thanks in advance... -scott