For those of you having problems with "null" loading file... this is what I have found to make it work.
First of all, wonderful MOD. I am of course trying to do my own thing so I am learning how to use benitomuso's Total Modder with a TFM412 pack, it is taking a while because I am installing one pack at a time, but it is working. When I got to TFM412 Pack 09 I hit a problem... (BTW, using that on top of ModAct 5.3). Pack 08 introduces Jet War and Pack 09 introduces Cold War era planes, and the Yak-36s are in that pack (it is the v 2.5)
At first I could not see either of the Yak-36's in the plane selector... I made sure that the HD mod was on, but nothing, so I made sure to overwrite the two dlls (il2_core.dll and il2_corep4.dll) with the mod ones... and you need to make sure you have the right ones, because they all seem to have the same size, so I used the ones dated 03/01/2013. That fixed being able to see the planes and loadouts...
However I was getting a "null" error on loading the mission. I looked at the log file and saw that the error was ID 4, and it had something to do with the "yak36" flight model data file. I tried flying a MiG-21 and all was good... it was only the Yak-36... so I tried in vain all different versions of the "yak36" flight model file in the Mod... same results... after reading a few of the posts here, concerning the ModAct flight engine version I tackled that.
Total Modder loads mods in order, and I had the MOD ACT 5.30 activation files running before Engine version 2.7... Once I had Engine 2.7 loading before the MOD ACT 5.3 files then I was able to fly both Yak-36's. Makes sense since the first occurring version of a file is the one that will be loaded by Total Modder, so the engine files are newer than the ones in MOD ACT 5.30... for those not going through the same process, to overcome the "null" loading, the key truly is loading the latest MOD ACT engine on top of MOD ACT 5.30. The latest engine version is 2.7.
Hope this helps.
UberDemon/danzigzag (DZZ)
www.uberdemon.net