Hi Matt,
Good to see that your problem is resolved this time, but when I saw your post I could spot the real cause in eight words: "I spent several hours working on a sketch".
No sketch in Pro/E should take more than a few minutes. Good modelling practice in Pro/E is to use many, simple features rather than one complex one; a simple guide is that a sketch should have no more than about six entities or dimensions. As with everything this is a guideline not a rule, but it's a good guideline.
Depending on what you're doing, you should either build up your model (casting / moulding) from simple shapes, or cut it away (machining) from a simple 'blank' - or sometimes a mixture of both. Features such as grooves, slots, holes, ribs, pockets, chamfers, rounds should all be added individually, and late (the smaller / less important the feature, the later you add it). As you add later features, you can reference major surfaces (or edges, or vertices if it can't be avoided) produced by previous features, so you shouldn't need any duplicate dimensions.
I gather that this is different to some other CAD packages, but it works really well in Pro/E, both for making stable models when you come to change them later (the wonders of parametrics!) and also just to make it easy to find a dimension when you want to change it, or to delete a feature that's no longer needed.
There has been extensive discussion in the PTC/User (http://www.ptcuser.org/) list - if you're not signed up, it's probably worth doing so just to search the archives. Alternatively, maybe some people on here would like to post their lists of 'best practice' - I have a few, but don't want to distribute other people's work.
Good luck!
Jonathan
