What does any but in following context?
But the chief fault of ancient systems, such as the Roman, was that computation with numbers was so difficult that only the specialist could handle any but the simplest problems.

Question

Answer

I presume that the writer wants to say this:

Most ordinary people could only handle the very simple problems, while all of the other problems had to be dealt with by the specialist.

It's expressed in a very confusing way, though. It's given me a headache just thinking about it!

Answer

The meaning is what you would expect, even if the order is a little strange. 
'...any problems other than the simplest ones'.