Esporadicaly I get an "Unable to read sector on C:, Retry,..."
I get this error when I try to open a btrieve file. Does anybody have the same problem???

Considering that Btrieve 5.12 was probably released in 1990, I'm not suprised it's giving you trouble. What OS are you using? You might want to run Scandisk and Defrag to make sure there aren't problems with the hard drive but if Btrieve is the only program having problems, you'll probably want to upgrade to the current version. For more information visit http://www.pervasive.com

I'm using DOS 5.0. I can't upgrade at this moment. Could it be apoblem with the .pre files? or page sizes?

I doubt it's a problem with page sizes. It could be an issue with .PRE files but those should be recreated everytime the engine is restarted. You might still look at checking the hard drive for sector errors.