Chris

sometimes, tab object is missing, even in maxmsp windows (preferences by e.g.)

tab-no-such-object-maxmsp-503

Be sure that you don't have anything in your search path called 'tab'. Also, trash your preferences:

~/Library/Preferences/Max 5 Preferences Folder

c:Documents and SettingsYour usernameApplication DataCycling'74

Please note that "Application Data" is an invisible folder and may need to be made viewable.

Do you get any errors in the Max window on startup? When you try to instantiate a tab object and it doesn't show up, are there any errors?

Be sure that you don't have anything in your search path called 'tab'.  Also, trash your preferences:

Mac:
~/Library/Preferences/Max 5 Preferences Folder

Please note that "Application Data" is an invisible folder and may need to be made viewable. 

Do you get any errors in the Max window on startup?  When you try to instantiate a tab object and it doesn't show up, are there any errors?