how to resolve it in Excel

hi ,

I have Created a package for dynamic loading of excel  file  in  2005.

in Expression  i have given "Connection String" and value is  "@[User::FileRoot]+ @[User::FileFolder]+ @[User::Filename]" and  while saving package its showing error as

Error: The result of the expression "@[User::FileRoot] + @[User::FileFolder] +  @[User::Filename]" on property "ConnectionString" cannot be written to the property. The expression was evaluated, but cannot be set on the property.
[Connection manager "Excel Connection Manager"] Error: The connection string format is not valid. It must consist of one or more components of the form X=Y, separated by semicolons. This error occurs when a connection string with zero components is set on database connection manager.

Thank  u 

Sathiya.s