Tom suggest you always use RS274X when creating the gerbers. RS274X embeds all the info need into one file so as to do a photoplot. Pretty much all board-houses support RS274X.
Also when you are setting up your gerber output, there is a field to define "Undefined Line width" for each film layer you want to output. By default this field is set to Zero and that should be fine most of the time, but as a safe-guard I typically make that field a "1"
Normally Allegro is pretty darn good at scanning the design and generating dcodes for the shapes pads, lines etc using RS274X format, think if you use that format life will be easier for you.
I always use 274x, in fact, I don't know why this one reported the other format because when I went back into the file, the default setting was 274x.
For undefined line widths, I make the setting 8 for each layer.
Something strange was happening when I was making those gerbers. Yesterday, I had a few small edits to do resulting from the design review. I made the changes then generated the gerbers using the same method I did on Sunday. This time I had no warnings or errors. I didn't change a thing other then add and route a few new capacitors.
I have noticed another oddity. I need to document the steps to verify I can dupplicate it before submitting to tech. Let's say I'm in etch edit mode and routing. I then go and save the file (which I do fairly often). I then select F3 to continue routing, but I can not manually route anymore. I select etch edit, then add route and still can't route. I select placement edit, then etch edit, then add route and it is now working. It seems like after a save, I have to select a different mode then go back to the original mode and continue work. Again, I need to validate this, but I've seen it happen more then once.