Error when running CountPeaks

[idupanloup]

I get an error when using the CountPeaks function for one of my samples:

There are 14963 whitelist barcodes.
Import genomic features from the file as a GRanges object ... OK
Prepare the 'metadata' data frame ... OK
Make the TxDb object ... OK
There are 7  sites
Doing counting for each site...
Error in (function (classes, fdef, mtable)  : 
  unable to find an inherited method for function 'writeMM' for signature '"NULL"'
In addition: Warning message:
In .get_cds_IDX(mcols0$type, mcols0$phase) :
  The "phase" metadata column contains non-NA values for features of type stop_codon. This information
  was ignored.

Do you know what can be the problem ? (i saw a similar issue posted by another user, but did not find the solution) Thanks !