That's a weird issue. I don't know on which end the problem lays.

Since I updated to Mek9, MachineMuse's Modular PowerSuits omniwrench started to crash with Unexpected error/NoClassDefFoundError: cofh/lib/util/helpers/ServerHelper.

This is me using MPS omniwrench with Mek8 r267, prior to update:

Once updating to Mek9:

Tested both cases, in Mek8 and Mek9, twice, to be sure.

Probably it's not Mekanism's fault, once the error log says nothing about it. The Mek9 update might have exposed a left-over dependency in the MPS mod, which wasn't supposed to be there.

Already reported, with error log: MachineMuse/MachineMusePowersuits#720

Yeah, this is not on my end- all I can think is that Mekanism v9 now ships with the latest RF API. Let me know if I can help with anything else!