If the Error button in the Tab Mix Plus Options is visible, some of your extensions are incompatible with Tab Mix Plus. It is recommended you disable or uninstall the extensions in the list. Click the "Show List…" button to do that.
Conflicts have been reported with Ubuntu Firefox Modifications extension, so if you use Ubuntu, disable that one (you can read more here).
Conflicts with BarTab, Colorful Tabs and Tree Style Tab have been reported. Since all these extensions manipulate tabs, shouldn't be surprising. Don't panic, these conflicts are usually solved rather quickly, especially if good information is given (like errors in console, screenshots, steps to recreate, etc.). Feel free to post and provide as much info as possible.
Issues with MR Tech Toolkit have been reported with Firefox 22 and up. Those are not Tab Mix Plus problems but rather MR Tech Toolkit. There's really no reason any longer to have MRTT installed - it hasn't been updated for years. Some of its functions are now Firefox default, others can be replaced with other extensions. (More reading about this issues)