Hey Hector,
You can only import brainvision files (.vhdr) and Simple Eeg Format in cartool (.sef) .
Best solution would be to convert your file to one of those format. I think simpler would be .sef
In cartool, under help --> Cartool reference guide --> Appendixes --> Cartool File format --> sef you can have an overview of how such a file is written to disk.
If you're no able to write such a converter, I could have a look to write one in python if you provide me an exemple file
Best,
Victor