deploying the c# project using mssql 2008

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C#

SQL-Server

deployment

i ve been developing windows form application using visual c# in visual studio 2008 and mssql server 2008.Is it necessary to install mssql server 2008 in the enduser desktop separately ? my database file is in .mdf extensinon.my connection string in app.config goes like:
data source=.\SQLEXPRESS;Integrated Security=true;AttachDbFilename=|DataDirectory|\mydatabase.mdf
it works well on my pc.but when i install it to other and open it throws error as :"A database with same name exist or special file cannot be open or it is located in unc share." i ve checked the datadirectory and specified .mdf file is present there. please help me out!!