Error while restoring database in SQL Server 2008 R2 This error occurs while I restore database from .bak file


  A system assertion check has failed. Check the SQL Server error log
  for details. Typically, an assertion failure is caused by a software
  bug or data corruption. To check for database corruption, consider
  running DBCC CHECKDB. (Microsoft SQL Server, Error: 3624)


After this the Database goes offline and it property sets to Single User.
If SELECT @@VERSION &lt; 10.50.1746.0 then it is possible that the issue you are coming across has been fixed in a specific cumulative update, and can be averted by updating your instance.

The particular issue is described here:

KB #980832 : FIX: "A system assertion check has failed" error message...

The cumulative update is here:

Cumulative Update #4 for SQL Server 2008 R2 RTM

But I recommend applying the most recent service pack and cumulative update available (since they come with a slew of other fixes as well):

SQL Server 2008 R2 Service Pack 2

Cumulative Update #4 for SQL Server 2008 R2 Service Pack 2