ASP.NET - AjaxToolkit FileUpload suddenly quit working

I have an ASP.net fw4.0 site that uses the AjaxToolkit AsyncFileUpload control (v16.x).  The file upload suddenly stopped working in PRODUCTION.  After the fail the part of the control that shows the file name gets a RED background.

It works fine on my local machine in development.

It seems to be a javascript error but I can't get a single meaningful clue about what is happening.

The error reads: Server Response Error: 'Object reference not set to an instance of an object.'

There are no errors in the log files. The Event Viewer on the server has nothing.  My c# code traps nothing.

Any ideas about what is wrong or a way to find out?

UPDATE

I started checking the permissions on the IIS server and the target directory did not have WRITE permission. I don't know how that happened but this fixed it.

could be an issue with your code where you are killing the process

could be a services.msc issue on the windows server, have restarted/recycled IIS through IISRESET /FORCE from START > RUN > CMD (run as administrator)

additonally post your code and I can take a look...

have you changed any user permissions? are there service accounts being used anywhere?

It was the permissions on the "Upload" directory.
When I created the web site I copied everything BUT the "Uploads" directory because I didn't want all the files in it.
I then created the "Uploads" directory manually. MISTAKE!!
Why the F_ck can't Microsoft return a meaningful error message under those circumstances?!

Microsoft cannot produce meaning full error messages for all possibilities, it will make application performance suffer, the errors are generic and categorized with Error Codes to assist in multitude of categories within sub-categories of error handling.

I appreciate the annoyance and i presume you are not alone to be frustrated mate.

:) chin up.