[TYPO3] Display content elements in a tab menu (rgtabs)?

[Bing Du]

I'm following rgtabs's manual to create a page that has rgtabs inserted as
plugin.  The following message shows up when I check the page in the
browser.

TYPO3 Fatal Error: Extension key "xajax" was NOT loaded!
(t3lib_extMgm::extPath)

I don't see 'xajax' listed as dependency for rgtabs.  Anyway, when I tried
to import 'xajax' in the Ext Manager, I got the following error

Error: The datatransfer did not succeed. Error: MD5 hash of downloaded
file not as expected:
0ae5df1df1331ca711b62cff0e0a0739 != 70a6b101e421229c9199ee1ebfa64384

This is the first time I got error when importing an extension.

I can go find the .t3x file of 'xajax' as a workaround.  Just want to make
sure there is nothing wrong with the 'xajax' ext. before hand.

Anybody know?

Thanks,

Bing