STOP 0xC000021A in CSRSS After Attempting to Free an Already Freed Screen Buffer

ID: Q234658

The information in this article applies to:

Microsoft Windows NT Workstation versions 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3, 4.0 SP4, 4.0 SP5
Microsoft Windows NT Server versions 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3, 4.0 SP4, 4.0 SP5

SYMPTOMS

When you run a program as a service that constantly creates and closes consoles, the following blue-screen error message may be displayed when you log off the computer:

STOP: c000021a {Fatal System Error}
The Windows SubSystem system process terminated unexpectedly
with a status of 0xc0000005 (0x77f7d40f 0x187fd70).
The system has been shut down.

The parameters for the status 0xC0000005 can vary.

CAUSE

This problem occurs because a screen buffer owned by CSRSS is freed by a process. During the freeing process, the screen buffer's reference count is incremented. When the screen buffer's reference count decrements to 0, an attempt is made to free the screen buffer. Because the screen buffer has already been released (freed), this causes an access violation, which leads to the Stop 0xC00021A.

RESOLUTION

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or the individual software update. For information on obtaining the latest service pack, please go to:

http://www.microsoft.com/windows/servicepacks/

Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack

For information on obtaining the individual software update, contact Microsoft Product Support Services. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, please go to the following address on the World Wide Web:

http://www.microsoft.com/support/supportnet/overview/overview.asp

WORKAROUND

To work around this problem, lock the workstation or server instead of logging off. However, this may not be a practical workaround in certain instances.

STATUS

Microsoft has confirmed this to be a problem in Windows NT 4.0. This problem was first corrected in Windows NT 4.0 Service Pack 6.

Additional query words:

Keywords : kbbug4.00 kbfix4.00 NT4SP6Fix
Version : winnt:4.0,4.0 SP1,4.0 SP2,4.0 SP3,4.0 SP4,4.0 SP5
Platform : winnt
Issue type : kbbug