If a support guru was able to successfully install the app for you, then it does in fact sound like the problem was specific to your browsers cache.
All Internet browsers allow you to clear their cache or reset things back to factory default. When you uninstall an app, it can sometimes leave traces that cause problems when you immediately try and reinstall that app.
Rather than walk you through the reset process for your browser, the guru just installed the app in your shop for you from their computer, bypassing the caching issue.
In any event if it has installed correctly you are good to go, but if you encounter the same error when attempting to reinstall an app it is likely that doing a reset/clear will solve the problem for you. If not, we are always here to lend a hand.
Take Care!