asa and eeprobe are software packages developed by ANT Neuro. The eeprobe format consists of files with the following extensions:
The data in the *.cnt and *.avr files is compressed with a zip-like algorithm, which makes the implementation of reading functions more difficult. The original source code (C-language) is available at this page ANT Neuro Documentation and Download. Contact ANT Neuro support in case you need help to compile import/export functionality based on this source code.
The FieldTrip functionality for reading asa or eeprobe files depends on the mex files that are present in fieldtrip/external/eeprobe. The FieldTrip release includes these files as a service to the users, however, these files are not maintained or supported by the FieldTrip team. Any problems with the source code of the mex files files should be addressed to ANT Neuro's support.
It has been reported that FieldTrip does not allow to read large files (above 1Mb, in the specific case with a sampling rate of 2048 Hz and 33 channels). A workaround for this limitation is to export the data as .avr in asa (Version 220.127.116.11), after which read_eep_avr can read files above 2Mb with no problems. For exporting, you can use Menu Data→Write→EEG/MEG, then choose eeprobe, and make sure to change extension to .avr.