Message from Scott Guthrie (Microsoft)

My guess is that those are browsers that have cached pages in their client-cache and are re-validating the scriptresource/webresource content. You'll see this for a short period - after which your users client side caches will be up to date.  If you are still seeing this for awhile send me email (scottgu@microsoft.com) and we can help.

Thanks,

Scott

---- and an other comment of Scott

That is probably to be expected.  It is likely search engine traffic that was accessing your webresource.axd and scriptresource.axd handlers before failing when they try to request old cached versions.  You will see this for awhile until they switch to the new URLs.  If you check your logs my guess is that most of the requests are coming from the same IP address (which is either Google or Bing).

Note that the content coming from these resource handlers isn't really indexable - so it shouldn't impact your SEO driven traffic (since they weren't really user links to begin with).