Without knowing how your mission.sqm file originally looked, I couldn't say for certain what your problem was. However, it sounds like you probably put some code in the initialization field of the officer, but forgot to separate two or more separate commands with semi-colons. Probably all you needed to do was add a semi-colon somewhere. Oh well, too late.
"OfficerE" means that it's an East officer (e = east).
All units are classified as vehicles in the mission.sqm file.
As for why your mission doesn't load anymore, you probably didn't delete every line of code relating to the officer. Else, you have other units beyond #24, and you have to renumber the remaining ones. Or something. Someone else will have to clarify if this would be necessary, as I never delete units using a text editor since it's easy to mess up things.