having two primary partition

is there any problem with having two primary partition on same hard disk?
am having problem with backing up my vista using windows backup(windows complete backup method), i get "the specified number of volumes is invalid" error, so i think it may be because vista is setup as a logical because my other partition with XP on it is set as primary.
so am thinking to convert my vista partition to primary without touching the XP i mean without converting XP partition to logical, or it will convert to logical after vista partition is switched to primary?

There's certainly no problem with multiple primary partitions, you can have up to 4 on any disk. However, I'm not aware of any change in the permitted combinations on Vista when compared to XP, so I doubt whether that's anything to do with it.

I've also heard of this problem with systems which only have Vista installed, which again tends to point to the fact that your suggested solution is not going to cure anything.

In general, messing with Vista partitions in any way sounds like a recipe for disaster, as it appears to result in a corrupt MFT. If that's what you've done it is almost certainly the cause. I suspect it is a result of something Microsoft have done intended to prevent drive cloning.

You might get some extra info here but I can't be bothered reading it all to find out if there's a solution.

too late, i already missed up partition tables, am ended up with fresh vista, been installing all softwares since 2 hours