[PlasmaKrab]

At which level does the problem occur?

Can you load at some of the units but not all?
If so, the load capacity of the helos may have been changed. that would hint at some kind of tampering with the .obf files.

Did you follow the overall loading procedure? Click on the carrier/carriee unit, press 'L' or click the 'load' button, then select the other unit?
Did you make sure that both units were on the same hex?
I don't think the helo is required to be landed before loading up, but you may want to check.

Sorry if that sounds like gameplay-for-dummies explanations, but troubleshooting has to start somewhere.