We are occasionally (very small percentage of the time) getting the error"Unable to write to folder: {path}.  Please change the permissions of this folder or specify a temporary folder using TempDirectory property or setting temporary file location in web.config." where {path} is the path to the upload folder specified in the web.config.  Let me reiterate that uploading works in the majority of cases.  However we do see on a regular occurrence the error.

Using the Sysinternals FileMon utility to monitor the folder during the upload process I see that when uploading a file, it appears that the file "TempPathTest.txt" is written, and deleted.   I believe that this is a crude test of directory permissions.  What I am speculating is that when activity gets high on our servers, two people may attempt to upload at the same time.  In this condition, I speculate that the one user is successful in creating this temp file, while the other gets an error either creating or deleting the file. 

 

If my speculations are correct, I believe that this code will need to be updated such that each attempt to validate the directory permissions by the control within a thread utilize some random file name to make this a multi-thread-safe operation -- possibly by appending a GUID to the end of the TempPathTest file like the uploading and persisted file name patterns.

 

Please confirm or correct my speculations.

 

Thanks for your attention to this.