I have noticed the following errors in the IR practice questions of the GMATPrep 2.1 software and have already written to MBA.com to look into these errors. I'm posting these here for the benefit of the Forum members:
(1)Integrated Reasoning Question Code IIR000816
Please see answer solution, RO2, line 7. What is  7000 ? This is clearly an encoding error. It should read 15R + 4T = $ 7000
(2) Integrated Reasoning Question Code IIR000815
The solution says that option B is correct for RO2. However, despite marking B, the software has marked my answer wrong. The green tick is actually on option C
(3)Integrated Reasoning Question Code IIR000827
The solution for RO2 reads: " Since the low temperatures in 2008 are significantly lower from the best-fit line than the highest temperature in 2001..." The year should be 2007 not 2001!