Unity Crashes when Loading New Asset

Every time I try and import a new asset into unity, the finder window comes up and then unity crashes every time, but i can still import asset packages. I have also tried making a new project but it still happens. It has only started doing this today while i was working on a project. I am using the free trail of Unity 4.3.4 on windows 7.
Please help it is very frustrating.

what packages is it? most likely there is something wrong with the package