最后经过Sybase工程师证实这是一个bug，是2 bytes FP index convert to 3 bytes FP中途异常中断而引发的error.

Sybase's reply:

As per conversation, from the stack trace itself, it shows to me that there is memory error when the 3 byte FP index is trying to access on this table.
This give us some hints that your table is corrupted and would like to verify by sp_iqcheckdb, but finally the table is corrupted too seriously and could not able to run sp_iqchekdb.
The corruption of this table may have the following possible scenarios:
1) The load job is being killed by kill -9 in OS during loading and when the 2 bytes FP is in the middle of automatic converting to 3 bytes FP 2) The load job is being killed by CTRL + C during loading and when the 2 bytes FP is in the middle of automatic converting to 3 bytes FP 3) The IQ server is being killed or abnormal shutdown during loading and when the 2 bytes FP is in the middle of automatic converting to 3 bytes FP
Therefore, please don't try to press CTRL + C to stop a load job and fix the load problem after the load job is finished. Also, checking the iqmsg file after the load job finished to see is there any stack trace is generated also can help to prevent or fix the problem earlier when the problem happen.