Problem is at least temporarilyi solved: I started up Adobe Acrobat Reader 5.0 and it gave me a warning message something like--"You cannot open Adobe pdf files from within your web browser due to a configuration problem. Would you like to fix it?" I clicked Yes and it only ran a few seconds. When I tried the application where I had the problem, the pdf files opened OK but using Adobe Acrobat Reader 4. I have both versions on my machine. Still don't know what caused this problem, because it didn't happen at first after downloading ver 5.0.