Have you tried looking in Event Viewer for errors which approximate the times that you get these onscreen error messages?
What is the Event Viewer, and Should I Care - Ask Leo! - http://ask-leo.com/what_is_the_event_viewe...uld_i_care.html
If you find such, click on that line item for details and post them here...someone will try to help you sort it out.
<<The only thing is that since then I have noticed that I have trouble if my computer gets shut off and the wireless network is not disabled first.>>
Can you elaborate with some details re what happens? I guess that I don't understand why you should have to ever disable a wireless or cabled network.