Run the SFC
Windows XP, Vista 7 how to
Use the System File Checker tool (SFC.exe) to determine which file is causing the issue, and then replace the file. To do this, follow these steps:
Open an elevated command prompt. To do this, click Start, click All Programs, click Accessories, right-click Command Prompt, and then click Run as administrator. If you are prompted for an administrator password or for a confirmation, type the password, or click Allow.
Type the following command, and then press ENTER:
The sfc /scannow command scans all protected system files and replaces incorrect versions with correct Microsoft versions.
If this does not solve it, you may be infected, see this WIKI