Restoring issue,

Hi,

we have one database called (A) and one backup file(b.bak),

we are restoring the backup file into existing database(A) WITH REPLACE option  that time we are getting bellow error.

"The file 'C:\Program Files\Microsoft SQL Server\MSSQL10_50.N1\MSSQL\DATA\B.mdf' cannot be overwritten.  It is being used by database 'B'."

but B database is offline.