IPB 2.1.3 to vBulletin 3.5.2
 

I did a fresh install of vBulletin 3.5.2 onto my server, and then used impex to import my IPB 2.1.3 SQL data into vBulletin, well it did import all the correct data and everything, but users cannot login to their accounts using the password they had on IPB, is there some kind of process I need to do before being able to login, or is the conversion tool just not fully compatible.

Thanks in advance!

It's not really that it's not "compatible", it just isn't possible to convert IPB passwords to vB passwords due to the complex way IPB encrypts their passwords. It's a matter of IPB passwords being hashed and then salted on top of that, if that makes any sense, and there really isn't any way to decode it.

I was in your exact same shoes one month ago and unfortunately there is no way around it...What I had to do is send out a mass email to everybody with the Lost Password link in it so that they could reset their passwords that way...it sucks, yes, but you have no other option.