>>>> Database: H:\MI4\MI4_2.FDB
>>>> Index 1 has orphan child page at page 51974 in table ACC$PREDOC (133)
>>> Index ID and relation ID
>> Different IDs for table ACC$PREDOC (133 and 134) look very suspicious
>> to me. May be the author often drop and recreate the table?..
>
> After recreate relation can't obtain id less that was before...

So, it must be that between first error and the second he did
backup-restore.

Author! What is your drive H???

SY, SD.