Cannot drop publisher?

I want to drop an Oracle publisher from SQL Server (2008).

exec sp_dropdistpublisher @publisher='mypub'

However, I got the following error when executing the stored procedure. How to drop the publisher?

Msg 2812, Level 16, State 62, Procedure sp_dropdistpublisher, Line 194
Could not find stored procedure ''.
Msg 2812, Level 16, State 62, Procedure sp_dropdistpublisher, Line 204
Could not find stored procedure ''.

And `exec sp_helpdistpublisher @publisher='markit_sfprod'` returns no row. 

The following stored procedure called in sp_dropdistpublisher returns null for @distribdb. It caused the problem.

EXEC@retcode = sys.sp_MSrepl_getdistributorinfo    @publisher      =@publisher,@distributor    =@distributor    OUTPUT,@distribdb      =@distribdb      OUTPUT,@publisher_type =@publisher_type OUTPUT