Which script did you try installing? I'm not sure why it would give you a runtime error...but of course I'm computer illiterate! Sorry it took me so long to answer! Hopefully you get it figured out or someone else will come along and maybe be able to offer you some useful advice.
now chrome not allowing scripts to install outside of chrome store. so u can install the script by drag and dropping the script file into the extension. to do so open the extension tab by clicking on tools->extension. open new tab and open the script page and click install. it will download to the chrome default download location but chrome throws an error called 'scripts can be installed from chrome store only'. open the script where it was downloaded. drag and script into the extension tab. now chrome asks whether to add the script or not. click 'add'. finished.