Try this
STEP 1: Update your Anti-Virus Software to ensure that you do not have a virus
or trojan on your system.
STEP 2: Try running the SecuROM protected application in Windows 2000
Compatibility Mode:
To do this:
- right-click the dlcsetup.exe file of your application (the path to this file
is: C:/Program Files/Steam/steamapps/common/borderlands/Binaries/DLCSetup/)
- click on 'Properties'
- click on the 'Compatibility tab'
- mark the box called 'Run this program in compatibility mode for'
- select 'Windows 2000'
- click on 'Apply'
- click on 'OK'
STEP 3: Please re-start the SecuROM protected application.
If you encounter any strange in-game behaviour when running your application
in Windows 2000 Compatibility Mode, we suggest:
1) Disable all software running in the background (incl. Services) and start
the application in normal Mode (without Windows 2000 Compatibility Mode).
Also, be sure to disconnected from the Internet if you disable Firewall and
Anti-Virus Software.
2) Try running the application in a new Windows Account (without Windows 2000
Compatibility Mode), or
3) Try running the application on a clean installed PC