You are *not* a moron - this really should not happen. You are not the first....
In another thread (do a search for 'uninstall') Patric gave the following information:-
<<quote>>
installShield creates a directory where it keeps all the information on installed software. On my machine it is 'C

rogram FilesInstallShield Installation Information'
'InstallShield Installation Information' is marked as hidden so to be able to find it you have to change folder options on you PC to show hidden files. Search for files containing 'Europa' in this directory and you will find a file called 'setup.ini' with the following content:
[Startup]
AppName=Europa Universalis
Engine=0
Copy=1
Source=0
[Languages]
Default=0x0009
count=1
key0=0x0009
On my PC this resides in: 'C

rogram FilesInstallShield Installation Information{A6F1BDF7-53A7-4AF6-84B9-0C51C722BC91}'. I'm not sure if the last directory name will be the same on all machines but I think so. Delete that directory and you will be able to make a clean install.
Patric
<<Unquote>>
You may also have to look thro the registry and delete anything to do with EU.
Failing all that then it looks like a reformat is on the cards! Make sure you install the correct patch next time...