Hi, The problem is solved now. The bioperl 1.4 version is from the Trouchelle repo, but 1.6 is in the Bioperl Regular Releases repo. When I added all the repo according to the bioperl wiki instruction, somehow 1.4 became a prerequisite for 1.6. But when I removed Trouchelle repo (so removed the 1.4 version), the installation proceeded without errors.

Thank you all for the help and suggestions.

Best,