Older First Edition databases may have experienecd data related problems in the past. As software applications evolve, the tendency for newer versions of the application(s) to become more sensitive to these "legacy issues" caused by older versions. For example, a power outage causing a record to corrupt might now produce a problem that a newer version may detect, while the older version did not. This is due to ongoing quality control of the software products.
These messages are caused by a mismatch, or corruption, of records between the xxsub3.dat and xxsub4.dat files, where xx is the two letter publication code:
In other words, there is a record in xxsub4 for which there is no corresponding record in xxsub3. Xxsub4 is called an add-on file, it is simply an extension of xxsub3. xxsub4 was added several versions ago to hold data for a given subscriber due to the addition of new fields to First Edition. A simple way to force this to happen (for purposes of illustration here) would be to add a new subscriber then restore an older backup less the xxsub4 file.
It is recommended that each occurrence be logged (save a screen shot), then click Yes to delete the add-on. Since there is no sub3 record, there is no way to recover it. Re-enter as much of the subscription data as appropriate.