Here's a tip I saved from somewhere online (can't find it any more!) to allow ProStreet to work after you've installed Undercover, as it'll throw an error otherwise apparently (probably won't if you're using a cracked version, but I'm not!). This isn't my advice, andI can't say where I found it originally. Bu I'm just sticking it here to help people who may have missed it originally!

Bear in mind that the paths will change if you install either game elsewhere, of course...

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Prostreet won't run after Undercover Install (on PC)

On my system, after installing Undercover, trying to run ProStreet results in an error code EC 5531, probably a SecurRom error code. This is because both ProStreet and Undercover use the same name for the main program, NFS.EXE. You'd think that since this same issue occurred between Underground 1 and Most Wanted, both named SPEED.EXE, that EA would't make the same mistake twice but it's there.

The long way to fix this is to open the ProStreet cd-rom and run EASetup.exe and do a repair install.

However the issue is just a few registry entries for a single key, which you can edit using regedit.

For Prostreet the values are:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\ App Paths\nfs.exe]
@="C:\\Program Files\\Electronic Arts\\Need for Speed ProStreet\\nfs.exe"
"Path"="C: \\Program Files\\Electronic Arts\\Need for Speed ProStreet\\"
"Game Registry"="Software\\Electronic Arts\\Need for Speed ProStreet"
"Installed"=dword: 00000001
"Restart"=dword:00000000

For Undercover the values are:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\ App Paths\nfs.exe]
@="C:\\Program Files\\EA Games\\Need for Speed Undercover\\nfs.exe"
"Path"="C:\\Program Files\\EA Games\\Need for Speed Undercover\\"
"Game Registry"="Software\\EA Games\\Need for Speed Undercover"
"Installed"=dword:00000001
"Restart"=dword: 00000000

Undercover didn't seem to care about the registry setting, so you can leave it set for ProStreet and run both games.