You may try to attach the sample project without the assembly files, perhaps you have reached the upload limit and that is the reason you are not able to upload the file. Eventually, you can try to change the extension of the file from "filename.zip" to "filename.zip.png" which may trick the system to believe the uploaded file is a PNG.
The latest error message you have sent us, indicates that AJAX is still enabled on the page. Regarding this error, I would suggest to remove AJAX controls (e.g. RadAjaxManager, RadAjaxPanel, UpdatePanel) temporarily from the page and run the application again.
Also, I would advise double-checking the way data is bound to grid. You can visit the following article as a comparison: How to bind RadGrid properly on server-side
I look forward to hearing from you.