As a previous poster mentioned, Paradox can experience strange problems when the available memory on your computer is more than 16MB. (Odd though it seems, at one time 16MB was a huge amount of memory!) (The -extk command-line parameter, suggested previously, cobbles around this issue.) It can also have problems if you have a disk drive more than (gasp!) 2GB; also an unheard-of capacity at the time Paradox-for-DOS was designed.
As a general rule, I suggest that if you're still dependent upon a Paradox-for-DOS application, it is high time that you investigate replacing this app with a new one built for Paradox-for-Windows. Believe me, I do not make this advice casually. I mean precisely what I say, and understand fully the implications of it.
Thanks for the information. Actually I'm in the process of writing a new database app using Delphi, with the intention of upgrading to a client/server database, but we are still using the current pdox 4.0 application for a few of the processes.