SQL server 2005 Job fail

Hi experts
we have Scheduled a Job in SQL Server 2005 ManagementStudio enterprise edition SP2.

Sometimes it fails with error :
Unspecified error occured on SQL Server.Connection may have been terminated by the server [SQLSTATE Hy000][Error 0]. The step failed and job is failing



T-sql script of the Job

update ItemMaster_IN set SKUDescription=
case
when
len
(
  case right(SKUDescription,1)
   when '_' then ltrim(rtrim(SKUDescription)) + ltrim(rtrim(SysSKUCode))
   else ltrim(rtrim(SKUDescription)) + '_' + ltrim(rtrim(SysSKUCode))
  end
) > 50 then
left
(
  case right(SKUDescription,1)
   when '_' then ltrim(rtrim(SKUDescription)) + ltrim(rtrim(SysSKUCode))
   else ltrim(rtrim(SKUDescription)) + '_' + ltrim(rtrim(SysSKUCode))
  end, 50
)
else
  case right(SKUDescription,1)
   when '_' then ltrim(rtrim(SKUDescription)) + ltrim(rtrim(SysSKUCode))
   else ltrim(rtrim(SKUDescription)) + '_' + ltrim(rtrim(SysSKUCode))
  end
end
where
right(SKUDescription,len(ltrim(rtrim(SysSKUCode)))) <> ltrim(rtrim(SysSKUCode))

Thanking in advance,