It looks like the Kongregate API changed causing a possible loading problem. It's not clear whether it's a problem with their API or not. Possibly related, my save game is also gone. It looks like Kongregate changed the save location.
@Cosmix360: The reavers aren't invincible. If you look at their ability it shows they have 2 armor which means it negates 2 damage. So the best way to hurt them is with high damage towers like the sentry.
Shirazz, did you complete all 25 levels or just the last level? Perhaps you skipped one of the optional levels?
Also, make sure to disable any flash blocking plugins on kongregate if you're trying to get achievements.
@osanseviero: Can you explain how the walkthrough is wrong? Keep in mind you do need to use the Garbage Collector to clear some of the spaces. If you're still having trouble you can always switch it to the easy difficulty.
@blarghedy: I just uploaded version 1.8.2 which *should* recover the corrupt saves. The bug was caused by saving the game while it was still loading. If the game was saved again after that it would be fixed. However, if you have multiple saves or loaded a game with starting a level it would get corrupted.
annie034: Try leave the medics alone until the end of the level. If you're still having trouble try checking out the walkthrough.
Skyangelc: Where exactly is the walkthrough for level 25 failing?
captingray: I think someone else mentioned that problem. I'll try looking into this later.
jakewf: good question on why it's called Ghost Hacker. The story never really touched on it, yet another thing I forgot. Basically the character no longer has a body and only has their mind, or ghost left. The term is actually taken from the Ghost in the Shell series, although there's been numerous other cyberspace references to it.