I recently ran into a very strange issue with printing sheets in one project. A user reported the sheet views have been blocked by some very large object stretch a mile or so while he was trying to print.
I look into the issue and it appears to be that giant thing or whatever it maybe comes from the titleblock family. After opening the family and it looks perfectly normal at first. However, I notice something quite unusual from the project browser.
There are wall types, curtain panel and mullions listed on the browser. Typically, the only thing that can be nested within titleblock family are 2D families like annotations. If you try to load/nest other 3D families and Revit would simply reject that. In this case, walls, curtain panel and mullion, which are system families, are impossible to come in to the titleblock anyway. They could only exist and be created in the project environment.
What I find it even harder to believe is Revit was able to show those elements that are in use by using "Select All Instance" from the type.
The thing is I can't even see these elements as the titleblock doesn't have a 3D view nor you can create one. All I could do is to delete them.
After I got rid of all the possible 3D elements, I was hoping to purge them out for good. I got another warning again about "Last type in system family cannot be deleted".
I have no choice but to leave the types in the titleblock and load it back to the project. This is definitely the first time I came across with this bug in titleblock family but at least it works now. All the sheets are back to "normal" and they print just fine.
I have no idea how the curtain wall and its sub component got into the family in the first place, but sure I will look out to this behavior in the future.