For the last couple days I've had a problem with VMWare Workstation v.7.1.4 build-385536 where my left mouse click suddenly stopped working in my Windows 2008 guest VM.

I finally found the problem!

When dragging and dropping text inside the guest VM I was dragging outside the VMWare container. This is what caused the problem.

To fix it so that never happens again I've disabled the ability to Drag & Drop from the guest. You can set this in your virtual machine settings, under Options > "Guest Isolation".