When I export my PCB design to Extended Gerber (RS-74X), a Gerber file for the top solder mask is produced but, none for the bottom solder mask. The PCB is selected as a “two layer (double sided)”, “plain vanilla pcb”. Is there a setting I am missing?
Your best bet is to upload the sketch file (the .fzz file, upload is 7th icon from the left in the reply menu) so we can look at the sketch and perhaps see what is wrong.
Problem Solved! Reloaded FRITZING and all is working correctly! Note to self: Reload when in doubt.
That is why posting the sketch is a good bet. With the sketch I (or someone else) would have tried it and discovered that the correct masks were output indicating the problem was in your setup rather than in Fritzing.