I had the same exact thing happen on my RSM (Red Sea Max) two days ago. I took my skimmer out and cleaned all the build-up out of the chambers. I also did a 5 gallon water change and laid paper towels on the surface of the water to soak up all the film. That tank is running clean as a whistle now. When I cleaned the skimmer and fired it back up, it started churning out gunk like nobody's business.
I've done a lot of research on the RSM and supposedly they have very temperamental skimmers. Personally, I do an overhaul on my RSM skimmer about once a month. Also, be sure that if you're going to clean the skimmer with tap water, give it a rinse in RO or saltwater so you don't have a chlorine contamination. Also, when you scrub the skimmer, don't use soap, and don't use normal household sponges either... they have chemicals in them that are toxic to fish... I just use a clean filter pad to scrub it with and use tap water... rinsing it with salt water after I'm done.
Lastly, expect some microbubbles when you first fire the skimmer back up... they will go away over time... sometimes as quickly as an hour after you restart it after cleaning.
Hey, if you have any other questions and want to ask a fellow RSM owner, feel free to PM me anytime.