There is a lot to cover here.
by R. Proffitt - 5/2/12 7:35 AM
Workgroups on XP Pro are limited to about 10 connections before you see rejections like this. You said there are 30.
I wonder if the person who created this network can help you with this limit by having someone logout so you can get on? Then again this could be a DOMAIN and for that, there is something entirely different to do.
And if it is a Workgroup, the most common mistake is folk forgetting to create accounts on the other machines. Let's say your account name is JACK. Can you as JACK go to the machine that you want to connect to and on that machine (not across the network) log on as JACK? That machine may not know JACK!