Our chip files don't support transcript level data, they're designed for converting gene level identifiers to gene symbols. Transcript level identifiers are best handled through packages such as tximport which are explicitly designed to handle this sort of data. Once your data has been converted to gene level then you'll want to make sure that the IDs (likely starting with ENSMUSG at that point not ENSMUST) have had their decimal version suffix removed as well. Then it should work with our chip file.
-Anthony
Anthony S. Castanza, PhD
Curator, Molecular Signatures Database
Mesirov Lab, Department of Medicine
University of California, San Diego