What causes "lock request time out period exceeded" when droping a column?
Drop the table using T-SQL as then the query will not timeout but instead get blocked. Note down the spid of this query window (it should be visible in the bottom of SSMS, right next to username). Once this goes into "executing" stage, open another query window and do this,

use master
go
select * from sysprocesses where spid = &lt;spid of the query which is dropping the table\column&gt;


Look at the blocked column and note down the spid number. Next query to see who the owner of the spid is (this will tell you who owns the conflicting lock on this table).

select * from sysprocesses where spid = &lt;spid # from above blocked column&gt;


Once you identify this, you can use dbcc inputbuffer(spid) to find out what query/command it is doing that has taken a lock on this table. If you deem that query inconsequential, then you can kill it using kill &lt;spidnumber&gt;. After this your query for the drop table/Column should complete.

Updated: Try to drop column  ALTER TABLE table_name DROP COLUMN column_name;

Check this link: https://social.msdn.microsoft.com/Forums/sqlserver/en-US/77fc7e09-ed14-481f-89d5-d5e143dab7bd/trying-to-delete-a-table-in-sql-server-management-studio-and-getting-a-strange-error?forum=sqldatabaseengine