outlook express hangs up after a while

Outlook express seems to function correctly but after running for a period of time, which i can't yet determine' it ceases to connect to my ISP and also will not close, except after three or four (or more) attempts. On rebooting the 'ourlook express did not close down correctly' message appears and all is ok, for a while. The best option at present is to use in short bursts and close down immediately after use, if possible. The Microsoft Knowledge Base article 900930 seems to recognise the problem but it is impossible to read beyond the Introduction further in to the article.

Any ideas?

Processor Intel(R) Pentium(R) 4 CPU 2.40GHz
Processor Speed 2.34 GHz
Memory (RAM) 512 MB
Operating System Microsoft Windows XP Home Edition
Operating System Version 5.1.2600