TYPO3 Core

You must deinstall mbi_products_categories first, because it depends on tt_products.

Thank you, Franz.

This error is still present. I have just uninstalled sr_feuser_register with latest TYPO3 4.2svn.

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

Reason:
Another extension depended on sr_feuser_register, but this has not been entered in the ext_emconf.php .

well, then it's a problem of that extension

not a core issue