Some process or program has written characters to your database.hdr file. The file is 1 KB, if some program or process alters this file then the application database could be damaged.
Restore from a backup and continue working. If you have no backup then the database files in your books directory (the application database) will have to be examined.
Call Q.W. Support at 905-946-9460 for instructions on uploading your data if you have no backup.