This is where I got stuck as well. I was receiving the "Error, main version older" error. I know it has to do with updating the file within the PH44IMG.zip folder, but I don't know what to update it to. My phone is a post-ICS updated Sprint Design 4G.
OK not sure what you are doing but here is the scoop on what could be your issues...
Assuming you are a windows user (if on linux then use gedit as your text editor) u can not use notepad to edit any files inside the recovery zip file. U will need notepad++ and 7zip for this. Download them if you do not have them.
Now assuming you are in windows once again, download the Sprint recovery image or correct carrier image from ClockworkMods - Downloads - 2FastRoms
Now once downloaded you need to change the file name to PH44IMG.zip (now .zip is your file extension so if you are on windows you need to make sure you are not adding it to the file name and ending up with a PH44IMG.zip.zip file - hope this makes sense to you...in other words rename it to PH44IMG)
You need to know your firmware number (settings/about phone/software) copy the firmware number for this example I am using the USCC file but it should be relative to this explanation. On USCC the last firmware update was 2.12.573.7 so in turn once you have your firmware number record it somewhere for reference
Assuming you are in windows open the zip (do not uncompress, just open it) with 7zip and open the android-info.txt with notepad++
Inside this file is two important things you need to know and make sure they are correct, the first is the CID (carrier identification) if you downloaded the specific file for your carrier then this will be correct, and you dont need to worry about it. The other thing is the mainver: this has the current firmware number...this needs to match your firmware number so edit it if not correct.
commit your edits and exit 7zip and try loading that,....
If on linux archive manager is perfect for opening the compressed folder and gedit would do for the editing of the text file. Both should be included in your distro...