This will help you if problem is related to the specially Unit
In order for the unite operation to be useful, the specified solids must intersect. In order to unite sheet bodies, they must meet at their edges unless they have overlapping faces.
The target solid.
Minor word specifying that the target solid is united with the following object list.
List of solid objects to be united with the target solid. Maximum allowed in list is 1000.
Optional minor word indicating that a count of solid objects is to be returned.
Variable which returns the number of solid objects.
Specifies a label to which program execution jumps if an error occurs. Possible errors include: maximum amount of objects exceeded; illegal object specified; cannot unite opposed sheets; can't unite solid with sheet, etc.