It could also just be old. Polyester resins have a definite shelf life so if it has been sitting around for a long time, using the bare minimum of MEKP to kick it will take quite a long time if ever to cure.
Best thing to do though if you want to use polyester is just get a new can from Sig and skip most of the "crap" found in local hardware stores. Most times they're a slightly thickened version used for auto and boat repair. Especially if sold as a kit with the cheapo 6 or 8 oz general purpose glass cloth. To get the proper flow you would need to add some styrene monomer which is the proper reducer for polyester resin to get it to flow correctly. I have used clear casting resin in the past in a pinch. You can usually find that in an arts and crafts supply store (Michael's or Ben Franklin etc.).

As for epoxy, finishing resin is the tool of choice there. ZAP Finishing resin or if you want to buy some bulk stuff that is as good or better, $32 gets you a 1.5 quart kit from John Greer and Associates (Kit 300/21). Here's their website if you like...

http://www.jgreer.com/

Good luck.