Why can't I install MMC?

First reinstall SP6a, restart server. Then install NT Option Pack for IIS 4.0.
After you are done reinstall SP6a & restart server again.
I am sure IIS-MMC will work fine. when ever you make changes in IIS always reinstall the latest service pack.Do let me known if the above way worked.
Akash

You do NOT need to install the option pack. Are you installing the MMC from the Symantec CD's or from some other source? Basically what you need is to make sure your NT server or workstation has at least IE v.5.0 or above installed on it; then install the Symantec System Center CD and it will install the version of the MMC that it needs (if not already installed). If you start from the Symantec NAV CE CD#1, and start with installing the Symantec System Center from there it will walk you through all of the necessary steps to install the SSC. The CDs also come with a "Quick Start" guide (you can also print it from the CD if you don't have the preprinted card), and this will walk you through all the steps for installing the management console and its snap-ins as well as the software. If you need further tips, I've done this lots of times so feel free to email me at synergy@synoffsys.com. Hope this helps!

I would install SP6 again, just to make sure all is well. Then download just the MMC and install it:
http://www.microsoft.com/downloads/release.asp?ReleaseID=31691
(please remove any spaces).
Then install NAV.

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