Hi Claudio,
I am afraid that you will have to give us some more information as this is not a known problem.
On what OS do you have this installed?
Which version of Visual COBOL is this 2.2?
Does the debugging error occur on all projects or just this particular one?
Can you open one of the examples in the Samples Browser from the Windows Start menu-->MF Visual COBOL group and debug it?
Thanks.