I have MathCAD 15 (M030 [MC15_M030_20131216]) running on a 64 bit Windows 7 laptop with 8gb of RAM and an Intel Core i3 processor. When I run programs that reach a certain length, the whole block turns into a blue mesh. It still works, and the subsequent calculations are good, but I am unable to edit the block. It was discovered earlier today that I could get rid of it by pressing pg up or pg dn (not by scrolling), but it returns again. I've been able to perfectly run the code on every other computer I've tried it on. I've included a screen shot of how it looks and have attached the worksheet. Thanks in advance for any help.
