md5 errors in bf2 equate down to 4things normaly
1.you have cheats instaled that have corupted the files
2.malware on the pc such as viruses and spyware
3.hardware problem normaly memory related.
4.hardware conflicts

if it is cheat related you will need to uninstal the whole game and then reinstall and prey punkbusted and punkbuster havent caught up with you and dont do it AGAIN.

however if you are a legit player and not a l33t hax0r then we ned to look at the next few steps.

please go here and run these online scans

Housecall at TrendMicro
http://housecall.trendmicro.com/hou.../start_corp.asp
Make sure you tick Auto Clean

BitDefender Free Online Virus Scan
http://www.bitdefender.com/scan/licence.php
Make sure you tick AutoClean under Scan Options

Panda ActiveScan
http://www.pandasoftware.com/active...n_principal.htm
Make sure you tick Disinfect automatically under Scan Options

eTrust Antivirus Web Scanner
http://www3.ca.com/securityadvisor/virusinfo/scan.aspx

also please go so start > control panel > administrative tools > event viewer
have a look in both system and application and see if there are any warning splats and errors if there are can you post them back here
cheers