We use oracle 10g. We found the following error in a trace file:
*** 2012-05-07 11:50:56.421 ksedmp: internal or fatal error ORA-07445: An unexpected error: core dump [ACCESS_VIOLATION] [_evaopn2+153] [PC:0x1BBDFA9] [ADDR:0x0] [UNABLE_TO_READ]  Current SQL statement for this session:
We took a lot of time to find the cause of this problem but we've been unsuccessful. We were using 9i and it did not have this problem. It only showed up after we recently upgraded to 10g.
What is the problem? How can I resolve it?