If you are experiencing foaming even after following the the tips in the troubleshooting guide, it is extremely likely and common that you have over-carbonated your beer.
Over-carbonated beer contains more CO2 in solution than is stable at the given pressure and temperature. Any change in pressure or increase in temperature will cause this excess CO2 to come out of solution, causing excessive foaming and gas bubbles in the beer line.
Therefore, when carbonating your beer, do not “speed-gas” it by applying more than the dispensing pressure. There is no way to control the amount of CO2 entering the beer using this method! Apply the correct amount of pressure (typically 8 to 12 PSI) and let it sit for a week or so to carbonate. If you do want to speed it along somewhat, you can roll/shake the keg, but never exceed the recommended pressure of 8 to 12 PSI for your desired carbonation level. Most homebrewing books contain carbonation charts. If you believe you have over-carbonated your beer, you may be able to reduce the carbonation level over several days by pulling the pressure relief valve on the top of the keg to vent the gas. Do this several times per day until you have vented the excess carbonation.