Your sheet cut blade didn't disengage. Simply press the plate on the left side and lighly lift the blade holder to disengage it. If this happens again, you probably need to calibrate the sheet cut engage/disengage position.
karst41 - Perf cutting can done in either position as long as you set up the condition for the tool position that you're using. Doing it on the cut strip will wear out the cut strip faster, but tends to give a better quality perf cut. Doing it over the trough will work well if you take the time to get it dialed in right. Some people will do kiss cutting and perf cutting on the cut strip (just make sure that you're budgeting in a new cut strip every month or two and that you have the blade depth set right) and some do kiss cutting and perf cutting both over the trough - this takes time to get dialed in - Force is the key here. Both of these methods are faster than: Kiss cutting on the strip and perf cutting on the trough. Though you can gang up jobs and send all the kiss cuts at once and then send the perf cuts after changing the blade position.
There are usually many ways to get something done. It just depends on personal preferences.
Good Luck