[Solved] 0xC0000005 Access Violation: How to Fix?

My cousin keeps on getting this when he tries to start his Steam client:

"An application error has occurred and an application error log is being generated. Exception: access violation (0xC0000005)... "

What's going on here?

Thanks for the tip about memory... the error message made me think there was something wrong with my cousin's RAM, so I asked him to download and burn memtest86 onto a CD, boot from it and scan his memory. Looks like there's something wrong with one of his sticks! His replacement is on its way. Again, thanks!

Stop 0x00000050 or PAGE_FAULT_IN_NONPAGED_AREA

The Stop 0x50 message indicates that requested data was not in memory. The system generates an exception error when using a reference to an invalid system memory address. Defective memory (including main memory, L2 RAM cache, video RAM) or incompatible software (including remote control and antivirus software) might cause Stop 0x50 messages.

Possible Resolutions:

• If you added new hardware recently, remove and replace the hardware to determine if it is causing or contributing to the problem. Run diagnostics software supplied by the hardware manufacturer to determine if the component has failed.

• Stop 0x50 messages can also occur after installing faulty drivers or system services. If the file name is listed, you need to disable, remove, or roll back that driver. If not, disable the recently installed service or application to determine if this resolves the error. If this does not resolve the problem, contact the hardware manufacturer for updates. Using updated drivers and software is especially important for network interface cards, video adapters, backup programs, multimedia applications, antivirus scanners, and CD mastering tools. If an updated driver is not available, attempt to use a driver from a similar device in the same family. For example, if printing to a Model 1100C printer causes Stop 0x50 errors, using a printer driver meant for a Model 1100A or Model 1000 might temporarily resolve the problem.