Okay, I'm not getting this error when running just full bobs and mini machines by themselves. I also totally misread the error; the problem is that for some reason, either mini tank 1 or mini tank 2 are in the "pipe" fast replaceable group, instead of the "storage-tank" group. Not sure what mod is doing that or why, but I don't think it's bobs.
I've attempted a potential fix by forcing all mini tanks to be the same replaceable group, but there likely will still be errors (stemming from the changes of this unknown mod, and why it's set the storage tanks to "pipe" fast replaceable group). So tell me if v6.2.11 works, or if there's a new error.