Fatal error encountered during command execution

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C#

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MySQL

hai all..

am having problem while accessing throgh LAN:
it is taking much time for executing command and returning error message like
Fatal error encountered during command execution
but some times it is executing perfectly.. here i need to fetch details of students whose attendance is not submitted am using MySqlDataAdapter to bind data to grid view

select
  sid
 ,stdname
 ,rollno
 ,concat(rollno,' ',stdname) as stdrollno
 ,division
 ,'1' as attendance
from studentdetails
where branch='ELECTRICAL &  ELECTRONICS ENGINEERING'
 and semester='3'
 and division='A'
 AND course='B.E.'
 AND sid NOT IN (
  SELECT s.sid FROM `attendance` a, studentdetails s
  WHERE a.sid=s.sid
   AND s.semester=a.semester
   AND s.branch='ELECTRICAL &  ELECTRONICS ENGINEERING'
   AND s.course='B.E.'
   and s.semester='3'
   and s.division='A'
   and date='2013-08-01'
   and a.period='1')
 order by rollno

please help me out
thanks in advance..