My student is having a problem with one of his/her professors. Would it be okay for me to call the professor to straighten it out?
You may mean well, but your student is now an adult and should take responsibility for his/her own problems and issues, whether with a college roommate or a college professor. Throughout his/her life, your student will be confronted with a number of conflicts and the need for resolution. The college years are an excellent time for your student to acquire and/or enhance his/her skills in problem solving, conflict resolution and negotiation.
Encourage your student to make an appointment with the professor and to then sit down and calmly and rationally discuss the issues. New students are often hesitant to seek out professors, but after doing so once or twice, they discover that professors are approachable individuals who really want their students to succeed. If your student is unable to work out the conflict with the professor, advise him/her to contact the chair of the department or to make an appointment with the dean of the school or college.