pc installer

This behavior can occur when you try to install a program that is installed using Windows Installer. The following registry key contains a value of data type REG_EXPAND_SZ, and the string is null:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment

Userenv.dll returns an error message when it tries to process the value, and Windows Installer quits. The following example shows a null value:

Value Name: CLASSPATH

Data Type: REG_EXPAND_SZ

String:
A supported fix is now available from Microsoft, but it is only intended to correct the problem described in this article and should be applied only to systems experiencing this specific problem.

To resolve this problem, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, please go to the following address on the World Wide Web:

http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS

Source:

Error Message When You Attempt to Install Program Using Windows Installer (Q251274)

http://support.microsoft.com/default.aspx?scid=kb;en-us;Q251274

(REMOVE SPACES from the pasted URLs.)

Maxwell

If you could describe your issue in just a little more detail, I'd be able to more adequately answer. What OS are you running and what programs are generating this error? Were you just previously installing another program? If that is the case, it's possible the installer was still running.