unless you have 1000000 messages, it should not take that long. it seems like the progress dialog is stuck. Try doing something else on the phone and get back to txtract later on. The progress bar should disappear. In a similar case I came across myself, the file was properly generated but only the progress bar was spinning.
1.5 release of Txtract hit a performance glitch (better coding vs. performance dilemma), and it's already pinpointed and fixed. I'm working on updated version as I type this post. It should be ready shortly.