I actually just went through something similar today. The SSP that was
working for us stopped and I was unable to access it. Fortunately, I was
able to create a new one and it appears to function properly. Unfortunately,
I am unable to unprovision the old one without some sort of permission error
on my Farm Administrator account. In my case, I am not even able to sign in
as another user in the Central Admin page, and within the SSP Admin Page,
some links work while others I get Access Denied. It is all very odd, and I
am still trying to resolve it myself.
Bear in mind, I am using Kerberos, but I followed detailed instructions on
settng SPNs and for the most part everything seems to click. It was only
recently that this occurred.