Ok hmm... the main reason why a tweak or add-on won't work is because of conflictions w/ another tweak, add-on or theme. I know it's a pain... but try disabling all your tweaks & add-ons and then run Carrier logo tweak & see what happens. I assume you're running Winterboard as well?
I tried installing this tweak... and couldn't get it to work for the life of me. I went through every combination of possibilities I mentioned above , but to no avail. Could possibly be something wrong w/ the resprosity server or something. Not sure beyond that... sorry.