Humans, by nature, have a tendancy to oppose change. When I began to see how much I'd have to re-learn, I was skeptical too, it's just natural. Everyone is different, but I like to plunge in headfirst with a big project and then be forced to learn it all as I go through.
I find some people's biggest hurdles with learning .NET is trying to do things the way they would in VB6, whereas there are now developments which make it either totally different, or even totally unnecessary to write the same code.