Hello cutechat, I have tried your suggestion and no luck.

I found that it fails when the translated url includes the symbol ?

For example, in the next rule, I marked in red the part that makes it fail.

RewriteRule ^cypher/      /Testing/cphr/Default.aspx?id=28 [L, I] 

I note that the variable id=28 has no effect on my test page, so it could not be a problem in the page.

If I remove the ?id=28 in the translated url, the Ajax Uploader works fine. 

Regards