I have this error as well, and tried almost everything to correct it

I'm workin with dnn 4.4.0 and Asp ajax 1.0. 

i modified my Web.config, put the dll's in the bin directory, disabled compression, installed sp1 for vs web dev express. 

added the scriptmanager in the dnn skin , but it still does not seem to work. In a regular aspx page it does work. But on every page with the scriptmanager I get the error Sys undefined. 

When i turned off the compression I got some errors extra, all related to Sys.

This is my web.config:

My web.config had been removed, but i upgraded tot 4.4.1 and i don't have the sys is undefined error anymore.

Email me and i wil send it to you.

I had the same problem with MS AJAX v1 producing an error in DNN 4.4.1 - something about “Sys.WebForms.PageRequestManagerPerserErrorException”

I gave your dll a shot and it produced a runtime error:

“Only one instance of a ScriptManager can be added to the page.”

When I added the following lines to the <excludedPaths> section of the Compression.config file the problem went away:

    <path>ScriptResource.axd</path>
    <path>WebResource.axd</path>