Hi Ken,

 

Thank you for your reply.

No, a test page like that does not get the same problem.

 

Some more background information about my situation:

 

The CuteWebUI:UploadPersistedFile is part of a custom user control for uploading and resizing images, which is added to the page dynamically in the CreateFieldSet method of a subclass of DetailsView.

 

Used as just another control on a plain page, it works correctly. You can see it in action here: http://v3manual.clubwebware03.nl/uploadtest.aspx 

 

But when used in the DetailsView context, so dynamically added in CreateFieldSet , it's getting the error I started this forum thread about. 

 

But... I do not always get that error. Sometimes it works just fine. I can't put my finger on it... that's why I'm asking for help.