[SQLCODE: <-400>:<Fatal error occurred>]

Dear,

  From time to time I get the following error after executing a select statement:

[SQLCODE: <-400>:<Fatal error occurred>]
[Cache Error: <<UNDEFINED>Main+65^%SYS.DBSRV *%qsc(1187,8)>]
[Location: <ServerLoop>] InterSystems.Data.CacheClient.CacheException [SQLCODE: <-400>:<Fatal error occurred>]
[Cache Error: <<UNDEFINED>Main+65^%SYS.DBSRV *%qsc(1187,8)>]

After repeating the query, the query succeeds.

How do I start debugging this type of issue?

Thanks,

Bart