wow, you gotta be in your middle to upper 40s now ! Isn't it too late to do an MBA right now ? or I bet it's for a PhD. anyways, as I've always believed: getting a low score in GMAT or GMATprep indicates a great room for improvements. So that's good news.
Go over the basics for math and verbal:
Math: try the kaplan math workbook
Verbal: definately the MGMAT SC
book + crack the GMAT from PR or the full MGMAT series
Overall: get the OG11
-math, and reinstall GMATprep and take the tests over and over again for more practice.
Good Luck !