Had this happen to me this week.  Everything was working fine on Thursday 
when I left for a three day weekend.  I took my laptop home with me.  My 
PC used DHCP.  The lease length on our network is set for one day.  So, 
while I was out, the server reissued my IP address to someone else.

After getting my old IP address back, that error no longer appeared.  You 
should be able to check what your old IP address was by uninstalling front 
page extensions then reinstalling.  If you left the default addresses in 
there, you should see the old IP address.

I tried reinstalling front page extensions with the new address, it did 
not fix the problem.  Something with old address is sticking around.