question

hi, My application has the following flow: 1. Acquire an access token (I have not implemented reusing tokens yet, so for testing I just get a new access token each time) 2. Use this access token to create a hierarchy of folders 3. upload files into the leaf node of the above. The problem is that I can upload one file and the next one gets a 401. Obviously the access token was just acquired so it can't have expired already, can it ? Any ideas ? thanks.