Activesync 4.5 no longer recognizes

you have to install windows 6.1 on your phone to get it to work again

I had the same problem. This problem is prevalent on Verizon phones as I have figured out online. I had the same issue as well.

Here is how I fixed the problem:

Go into Start -> Run (type regedit.exe) [Hit Enter or click on OK] -> HKEY_LOCAL_MACHINE -> SOFTWARE -> Windows CE Services.

When you get to Windows CE Services, click on it and the look into the viewing panel. Look for GuestOnly. Double click on it. A prompt will come up to Edit the DWORD Value. Change the Value data from 1 to 0 and then press Enter or click on OK.

When you connect your device, it should be fixed. You computer will prompt you to set up a partnership between your phone and the computer.