Call of sub type failiure, how do i register/check it?

I've writen some code in the solidworks api and i have a line i wish to check if it goes through.

swModel.InsertOffsetSurface 0.01, False

it makes an offset surface on the face im currently on, but sometimes it is not posible and i get no indication of it. How do i check if it went through?

the code around it looks like this:

Do While Not swFace Is Nothing Set swEnt = swFace 'Select through Entity bRet = swEnt.Select4(True, swSelData): Debug.Assert bRet swModel.InsertOffsetSurface 0.01, False swModel.ClearSelection Set swFace = swFace.GetNextFace Loop

Thanks in advance!