550 Directory in use by earlier version of Paradox.
Problem: Getting error "Directory in use by earlier version of Paradox."
When opening a table.
Date: 17 February 2005
Versions: All
Solution by: Bill Todd
Prior to Paradox 4.0 for DOS there was only one lock file named Paradox.lck. In 4.0 for DOS the locking mechanism was changed to improve performance and the new lock mechanism uses the PdoxUsrs.lck file. However, because the two locking systems are incompatible Pdox DOS 4.0 and later also creates a Paradox.lck file with a directory lock in it to prevent an earlier version from accessing a database that is being used by 4.0 or later.
Pdox DOS 4.0 and later also checks on startup to see if there is an existing Paradox.lck file that indicates the directory is being used by Paradox 3.5 for DOS or earlier. If a later version finds a lock file indicating that the directory is being used by an older version it displays the error message your client got. Apparently you have a corrupt Paradox.lck file that looks to the BDE like it was created by Pdox DOS 3.5 or earlier.
Delete all of the .LCK files in the data directory and the problem should go away.