We highly recommend working with your database administrator as they can easily help find the root cause of the issue with you.
The most common cause we have seen is the use of non numeric data. You can use the following SQL query to test for this:
tdata – THEIR CHARACTER JOIN COLUMN
,CASE WHEN (POSITION(' ' IN TRIM(tdata)) > 0) OR (UPPER(TRIM(tdata)) (CASESPECIFIC) <> LOWER(TRIM(tdata)) (CASESPECIFIC))
ELSE 'Numeric' End
ORDER BY 2,1;
Once you remove any bad data or fix the format issue, this issue will be resolved. Again, the resolution will be very specific to your data and environment, so it is best to work with your company's DBA to resolve this.