Installing an update via the CurseForge launcher will indeed download the new version, but fails to delete the existing old version. This means you end up with two copies of the same mod (but different versions), but that of course means the game will fail to load.
This happens whether you run the app as an administrator or not.
Update: Support has replied to a support ticket to say they are aware and a fix will be rolled out soon.
Thank you very much for contacting us, I will do my best to assist you with CurseForge :) We are aware of this bug and will be releasing a fix in the next couple of days. In the meantime, you can manually delete the file from the folder. Sorry for the inconvenience!