Sometimes when you try to remove a Content Type’s association from a list, you will get the error "Content Type is still in use", even if you don’t seem to have any items in the list!
Here are a few things to check:
- Make sure that the Content Type isn’t the default – Go to the list settings and under the Content Types section, click on the ‘Change new button order and default content type’ link. Be sure that the Content Type that you want to delete isn’t in position one, which makes it the default Content Type for the list.
- Empty the Recycling Bin – If you have deleted items that are based upon the Content Type you are trying to delete, you probably won’t be able to delete it. At least clean out the items that used it, and don’t forget that there are two levels of Recycling Bins (Site and Site Collection).
- Make sure that others don’t have items associated with the Content Type that you can’t see – This usually will happen in Document Libraries. Go to the list settings and click on the ‘Manage checked out files’. You may see some items listed that belong to other users which they haven’t checked in. Assuming that it is appropriate, take ownership of those items and then you can delete them.
All this assumes that you are a Site Collection Administrator, since you probably wouldn’t be doing this if you weren’t. If you aren’t a Site Collection Administrator, then send these pointers to someone who is and have them check things for you.