Track lines between letters letters when laser engraving

I bought a little chinese laser engraver. I am using Grbl software and it seems to work OK, except it leaves path lines between letters. I am using aspire to create the toolpath but I am not certain which format to save it in. Aspire provides a long list of formats in which to save the toolpath. It calls for .nc but I don't know which one. Would choosing the wrong format cause these lines to show or is it Aspire. I am not very experienced with this so please excuse any poor terminology.