Data Execution Prevention

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If the first option is already checked, put a check next to the second option instead "Turn on DEP for all programs and services except those I select" and then click Add to add the programs that you do not want to use the DEP feature. Then click OK twice.

Data Execution Prevention (DEP) is a set of hardware and software technologies that perform additional checks on memory to help prevent malicious code from running on a system. In Microsoft Windows XP Service Pack 2 (SP2) and Microsoft Windows XP Tablet PC Edition 2005, DEP is enforced by hardware and by software.

The primary benefit of DEP is to help prevent code execution from data pages. Typically, code is not executed from the default heap and the stack. Hardware-enforced DEP detects code that is running from these locations and raises an exception when execution occurs. Software-enforced DEP can help prevent malicious code from taking advantage of exception-handling mechanisms in Windows.

The cause of your problem is because some programs do not support DEP.