The transaction log for database 'tempdb' is full due to 'ACTIVE_TRANSACTION'

I had the same problem and it went away when I had increased Log Size of 'tempdb' database (Initial Size). (you can use SSMS and choose Properties of 'tempdb' database)

You can search all the temp objects with a simple SELECT * FROM tempdb..sysobjects WHERE name LIKE '%AllClasses%'
To fix it just run once:

BEGIN TRANSACTION
    DROP TABLE #AllClasses
COMMIT TRANSACTION

If you still cant delete it just check for zombie sessions with SELECT * FROM sys.dm_exec_sessions and kill it with KILL session_id.

With regard to the table drop issue, I have seem this happen when a nested procedure call has a temp table with the same name as a temp table in the calling procedure.
I have also very occasionally seen orphaned spids where a temp table is sort of in a zombie state, and doesn't match when you check the objectid. If it's the former issue just rename the temp table.
I would also check active spids and see if there are any hung transactions which could also be the cause of the transaction log issues, then kill them. The view is sys.dm_exec_sessions to see what's running.

This error happens when you are doing onerous queries on the DB before a commit performs.

For example, if you try to make a subquery with some analytic calculations over a table with millions of records and then you make an update on it, the tempdb grows in dimensions (because of the necessary calculations) until it reaches the maximum dimensions, giving that error.

The possible solutions are:

• Reduce the operations in segments wherever possible, for example making an update on a reduced set of rows (based on some keys)
• Increase the dimensions of the tempdb (obviously if there's enough disk space)