You seem to be using some nonstandard math fonts, probably some package that is supposed to set them up, but the corresponding support files that provide the right kind of information to the NFSS system aren't on your machine or can't be loaded for some other reason. In other words prior to that error that you listed, there should have been earlier errors or warnings that would/could give a hint of what is going wrong.
Basically if you intended to use a different font setup it is not enough to add a package you also need to ensure that
- the fonts are on your system (in a place where they are found by the engine)
- the corresponding .fd (font definition files) are on the system
If the latter are not found then NFSS will try for substitutes but especially with math involved those often do not work well and so you'll get this kind of error just before the engine gives up