wsp deploy error

I tried to deploy a wsp to my sharepoint site. 

I applied the ;

Add-SPSolution –LiteralPath "C:\wspName.wsp"

after that, 

Install-SPSolution –Identity wspName.wsp –WebApplication http://portalAddress –GACDeployment

but it gaved me an error such as;

this solution contains no resources scoped for a web application and cannot be deployed to a particular web application 

any suggestions?