Sorry if I am mistaken. I never tried this out but as per the MSDN article

http://msdn.microsoft.com/en-us/library/ms177456.aspx it says this

The data rows of the disabled clustered index cannot...

this was because i think first u should remove the subscriptions clean it and then only drop the publishers and distributers

u are telling that u have run sp_drop mergesubscription command...