Networking Engineers check this one out.

Got one for you almighty networking engineers.
A network with about 50 users.
(3) workstations out of that (50) loss IE access after say 10-20 mins after booting.
No other users have this issue. Yes there are servers and routers and DSL.
There are no viruses found by the most udated version of Norton Corp, no Unknown objects found by Ad-aware or Spybot. All MS updates applied.
Two of the three are somewhat older systems (P400) the other is relatively new (P800 or higher). Oh and by the way they can continously access other resources on the network, just loss access to IE. Any Ideas.