Eclipse 2.2 is meant for 902 so no that's not the issue.
The terminology when using Safestrap is important. The "Safe" side is actually the secondary partition where you can install experimental ROMs and mess around with customization without concern, because you still have the other partition as your backup. It's important to note that you can not flash ZIPs when you are on the other partition (aka "Safe System: Disabled" at the top of the recovery screen) because they don't want you to be able to mess this partition up. So you did say you were trying to flash it on the safe side which is technically correct, but I'm just making sure you didn't misspeak. In the event that you actually are trying to install this on the first main partition, that's why it's telling you it won't flash, you're not allowed to. It confuses people to consider the first/stable/backup ROM to be the "unsafe" one, but what it really means is "unsafe to F around with this partition". The "safe" one is actually the partition where you can flash things.
This may not be the problem in your case but just want to clarify that before we diagnose any further.
So make sure when you first boot up the phone, the Safestrap screen that pops up should have text/icons in the color GREEN and it should say "Safe system enabled". If it does, you should be able to press menu to enter the recovery screen and flash from there. If the text is red and says the safe system is disabled, you can't flash over this partition, and you need to go into the recovery menu, go into safe boot menu, and switch over to the other partition.
To get even more confusing, if you actually do want Eclipse to be your "unsafe" ROM (since it is pretty stable) and you want to have the other partition for messing around with ICS ROMs or whatever else, then you would need to uninstall Safestrap, switch to a plain recovery like bootstrap, install Eclipse as your ROM, THEN go back to using Safestrap, it'll recognize Eclipse as your first partition, and then create the second partition for installing whatever else.