Hello Andrew:

Rather than checking on start-up (because speed is an issue there), 2 checks could be performed each time a user clicks Print/Preview on a specification-type screen:

1) Has a specification been selected (ie. selection box is not blank)?
2) Does spec file exist?

In the world of "essential" versus "merely-nice-to-have", this is definitely closer to the latter, but it would be fast enough to be imperceptible to the user and would prevent error messages.