powershell can't recognize the vairable setting for dtexec.exe

when I run dtexec.exe in powershell,the value after ";" is treated as a cmdlet and throw a exception" not recognized as a cmdlet, function, operable program, or script file".

This script can execute under cmd-line, but not in powershell.....

dtexec /f "C:\Users\Administrator\Documents\Visual Studio 2008\Projects\Integration Services Project1\Integration Services Project1\FileCopyPackage.dtsx" /set \package.variables[User::SourceFileName].Value;"C:\sharefolder\ssiscopied"