this problem may be caused due to the improper active sync connection settings.
open the microsoft Activesync. then under the File Tab click Connection Settings.
then a winwow opens where you could see an option to choose .that is something like this -
This Computer is connected to
and the options are 1)Automatic 2)Work Network 3)The Internet
THe option you have to choose is option 1 ie Automatic.
this should work coz i used the same setting for the connection mentioned .