When I try to install get_player I get the following error message

Windows cannot access the specified device, path or file. You may not have the appropriate permissions to access the item

I'm using windows 7. I've tried installing as an administrator by right clicking

Can somebody help me to find a solution.

Thanks

You could try the steps outlined in this troubleshooting document:

http://support.microsoft.com/kb/2669244

Make your first step to download a new version of the installer from the following link as sometimes installers get corrupted during download and this can be the simplest but seldom tried fix:

Windows 7 and 8 get_iplayer installer (single .exe file)