Hi I am calling a query rule through an expression rule in dashboard. I am

In my experience, this is usually related to the query rule timing out.
Check out the standard output logs for the day you received this error (e.g. jboss1-stdOut.log.2014-09-03).
Search through that for the query rule in question. The stacktrace should indicate the source of the error.

it happens because of session timeout. logout and try again..

Just like Colton mentioned this has to be investigated at the application-server.log level.

In order to troubleshoot issues where the message is very generic such as: "Unexpected error executing query" you need to reproduce and then find this error in the application-server.log, once you have identified it review each of the individual "Caused by" clauses. Usually the most bottom ones (that belong to that error) will be the most informative ones in the stack trace.

Query rules do not fail due to session time outs since they are evaluated at the server side.

We are talking about a possible time out of the query itself in the database engine, or an issue with the column mappings, etc but again, the best way to determine the root cause is looking at the "Caused by" clauses of the error in the application-server.log

Any Suggestion as to how this issue was resolved ?