fixcat.bat path-to-corrupted-catalog path-to-new-catalog.dat
As you will want to rebuild a catalog.dat file in the same location as the corrupted file, rename the corrupted file before running fixcat.
rename C:\myFiles\CATALOG.DAT C:\myFiles\CATALOG.DAT.bkup fixcat C:\myFiles\CATALOG.DAT.bkup C:\myFiles\CATALOG.DAT