That sounds like a problem with the CellML reader then. Open an issue there with the file you’re trying to read. Do you also have the SBML from the SBMLBiomodels repository? That could be a possible way to read it in: the CellML reader has had less work than SBMLToolbox.jl
There was a version of MTK which was passing an argument that it shouldn’t’ve. That got cleaned up and the latest versions should be fine if you upgrade.