One way of fixing this is to go into dial-up networking and set up a new connection with the identical properties as your current one. Set this one as the default and check to see if it works. If it does, you can then safely delete the old one.
I have just cured this problem on my PC,I removed all the installed communication files in setup,re-started then re-installed them(control panel/add remove progs/windows setup. This was after trying out all microsoft solutions, which did not help