What Is Windows Protection Error 45?

The Error
Protection Error 45 refers to a problem with 'memory protection.' In a modern operating system, such as Windows, different programs are given different chunks of the computer's memory, or RAM, to work in.
'Protection' Explained
'Protection' in this case refers to the operating system's ability to mark those sections of memory as being separate from one another. If a program finds itself needing more memory for a task, it's supposed to ask the operating system to move things around to give it more space. When a program somehow finds itself with problems accessing the memory it's been given to use, it is experiencing a protection error.
The Cause
Generally, every version of Windows since Windows 95 has had a fairly effective memory protection scheme. Since the release of Windows XP, that scheme has been virtually foolproof when dealing with software that follows the rules. Unfortunately, this means that the most common cause of protection errors in any version of Windows since Windows 2000 involves hardware. RAM does occasionally go bad for no obvious reason, and it's the most common cause of this error.
The Solution
If some of the RAM in your computer has gone bad, generally you must replace the RAM. But there are things that you can do before you take your computer to be repaired. If you're comfortable doing so, you can open the computer and re-seat the RAM. The contacts between a RAM card and the rest of the computer can foul up, and sometimes all that's needed is to remove and replace the RAM.
Memtest86
You can verify that the problem is with the RAM itself by running Memtest86 (see Resources). Memtest86 is a program that you burn to a CD and run in place of your normal operating system. It will run thorough tests on your RAM and tell you if a memory stick is bad.