I have a user that has IE8 on a 64-bit Windows 7 machine, they are trying to check-out multiple documents at the same time by selecting all documents and the selecting Check Out up in the Documents tab. The 'Checking Out...' ajax notification pops up, but nothing is checked out. If he tries to check out a single document it works some of the time from the 'Check Out' option on the documents tab.
We have emptied the OfflineFileCache, cleared the Internet Explorer Cache, Tried repairing the office installation, and installed SharePoint Designer 32-bit to add the SharePoint support package.
Not sure what other troubleshooting steps need to take place.