aist-pskесть большая таблица около 18 млн записий, туда идут insert порциями примерно по 100 записий

очень похоже на ISAM Error -136:
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ISAM error: no more extents.

The database server needs to add an extent to a table but cannot do so. Either not enough disk space is available in the dbspace, or the table has been given the maximum number of extents that is allowed. The database server administrator can determine the cause as follows:
1. Determine the tblspace number for the table. It is the value in the partnum column of the systables table for this table.
2. Convert the tblspace number to hexadecimal and extract its most-significant 2 digits (the high-order byte). This chunk number indicates where the table resides.
3. Use the tbstat or onstat utility -t option to find out disk usage for this table. Note particularly the values reported for npages (disk pages available), nused (disk pages used), and nextns (number of extents).
If nused is less than npages, and nextns is large (over 200), the table has too many extents. The upper limit of extents per table is between 200 and 50. The limit varies with the table definition and the disk-page size in use. Reallocate the table using fewer, larger extents. Unload the table data to a flat file. Drop the table. Re-create the table, specifying a first-extent size sufficient to hold all its current data and a next-extent size between one-fourth and one-sixteenth its current size. Then reload the data into the table.
If nextns is small or the difference between npages and nused is less than the size of the next-extent size for the table, not enough disk space is available in the dbspace where the table resides. Use the chunk number from step 2 and the ON-Monitor or ON-Monitor Chunks display to determine the dbspace, then add a new chunk to that dbspace.
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Но, вообще-то, нужно именно see corresponding ISAM error, например при выполнении такой же операции в dbaccess, если уж самоделки его (error code) от Вас прячут.