By default there is no need to compact a Trash folder in Thunderbird. When you use the the command "Empty Trash" in the context menu, the "Trash" file in the profile is automatically reset to 0 kB. I know that many people use the Trash folder as a temporary folder because they fear to loose important messages by erroneous deleting and by emptying the Trash folder. So as time goes by they gradually delete messages from the Trash folder. This habit makes the Trash folder size increase until TB prompts for folder compacting. A Trash folder in Local Folders exists by default but is rarely used unless you use Local Folders for storing messages (e.g. Global Inbox). I don't know which is your case and prefer that you give precise info whether your Thunderbird is actually blocked or not. If this happens repeatedly at each compacting, I propose to delete the faulty Trash file in the profile and create a new one. You could also immediately try th R-click on the Trash folder > Properties > Repair folder...