Couldn't use VC6 after installing SP3

After I installed Service Pack for Visual Studio 6, i cannot start VC++, a
dialog box saying " Cannot load package 'devdtg' because its internal
version number, or the internatl version number of one of its components dos
not match the version of the Developer Studio shell. Do you want to
continue. " [OK]

After i press the OK button, it say "DEVDTG This required file cannot be
loaded. Please re-install Microsoft Visual C++ "

How can i solve that , and waht's the reason for that.

The service pack i installed was downloaded from Microsoft's web site, which is the full SP3 12 files (each about 12M, i think)

Thanx