I know your grief. I, too, had difficulty reinstalling Winfax Pro after I removed it from my computer. I kept getting the same error that you speak of.
In desperation, I contacted Norton, who took over Winfax Pro. They said they don't offer support, don't know who give it and did not seem to care.
I then started to just search the internet, hoping that I would find someone who could help. I happened to stumble upon GetFaxing at http://www.getfaxing.com.
I felt I had nothing to lose, so I signed up. The very next day, I was online with one of their techs who took over my computer remotely and with the many Winfax problem solving tools that they had, got the program reinstalled. I don't know what they did, but they even recovered my fax directory and my messages which I thought were deleted.
I don't normally post to message boards, but I thought the greatest tribute I could pay GetFaxing, was to tell others.
I know what I went through and know that this will help somebody else.
I don't know what made these people decide to start offering this technical support, but they are offering a much needed service. I can tell that from surfing the net and seeing so many people with Winfax problems and no help around.
You pay for their service, but they are very reasonable for the knowledge that they have. Besides, whatever it costs, it is better than taking your time trying things on your own and nothing works.
I guarantee they can correct your problem. I strongly urge you to contact them. Your worries will be over.