Answer 1
Where this master page is deployed ?
Is it ghosted in library or is it under _LAYOUTS folder ?
If you have publishing feature turned on, have you approved the Master Page in the master page library.
I believe it is missing a directive definition in the Master Page ?
Is it SP 2010 portal ? Are you trying to re-use a master page from SP 2007 ? Are you building your master page on V4.master ?
Please provide more details