I've said this many times before. Obviously I have not explained this well enough. Let me try again.
In *ALL* versions prior to 2.42.4 (including 2.36.7 I'm prettty sure) there is a serious bug with saved sim and dbo bot files which only manifests itself in long run evo sims. If a sim had run long enough for any bot to accumulate more than 2^15 bytes worth of mutation details (the string descriptions of what mutations have occurred in it's ancestry, this happens around 150 mutations) then any saved sim or bot will be corrupted. This bug had been in the code since long before I had ever heard of DB.
Any bot saved in binary format (as a dbo) would also be corrupted as saving a bot in this fashion (as opposed to just saving the DNA, which is fine) includes the mutation history and thus the corruption in pre 2.42.4 versions).
This is why nobody ran long run evo sims prior to 2.42.4. (Okay, this is not strictly true - you can run long runs evo sims prior to 2.42.4, but any saves get corrupted and fail to load.)
In 2.42.4, I fixed this problem for all new sims. Any newly created sim in 2.42.4 or beyond with newly created bots will save and load just fine with essentiall infinite limits on mutation details.
For already corrupted sims and bots, I did my best to load the sim or bot, working around the mutation details corruption. But a side effect of working around the corruption in 2.42.4 is to mess up the mutation settings for every bot which had exceeded the 2^15 byte limit. So if you load a pre 2.42.4 bot in a 2.42.5 sim and then save such a sim or bot, the messed up mutation settings get carried forward in the new saved sims.
In 2.42.6, I did more work here (just for you Testlund - well, okay, not really) so that I now default the mutation settings if a pre-2.42.4 sim or bot is loaded. So now, even loading pre 2.42.4 sims should work even better than in 2.42.4 or 2.42.5.
So, let me re-interate: this issue was a one time thing. If you have a corrupted sim or binary bot that ever lived in a pre 2.42.4 version, things should load just fine in 2.42.6, but the mutation setttings will be set to the defaults. (If you don;t trust me and want to be totally safe, save any bots in old sims as textual DNA and load them into a new sim created post 2.42.4).
That said, as a rule, saved sims and bots from one version should always work fine in the next. Any failure for them to do so is a bug.