What does Error: 1204, Severity: 19, State: 4 mean?
Explanation:

This error occurs when there are not enough system locks to complete the current command. SQL Server then attempts to obtain a LOCK block to represent and control the desired lock. When dynamically configured, the lock limit is determined by the available memory. When statically configured, the lock limit is determined by the sp_configure setting.

Action:

you have two options earthier wait for sometime and re-execute the same command(s), or reconfigure locks value by executing the following commands

sp_configure locks, XXXXXX     where XXXXXX value higher than the original one
GO
RECONFIGURE WITH OVERRIDE
GO


Regarding troulbeshooting this error please refer to the log and execute the following command:

SELECT @@SPID AS 'ID', SYSTEM_USER AS 'Login Name', USER AS 'User Name';


This will show you the needed info, and you can check Activity Monitor too

some useful links:
http://www.sqlservercentral.com/Forums/Topic141154-92-1.aspx
https://technet.microsoft.com/en-us/library/aa258769(v=sql.80).aspx