I'm curious as to the color coding that is used for v0.72.1 of SimPE.  Certain sims in my neighborhood show up in SimPE with red backgrounds, others blue and others gray.  I know what the blue and gray backgrounds mean, however I'm uncertain as to what the red backgrounds indicate.  I know that one of my sims has a red background and whenever I go onto the lot, there is an error with him and I get endless error notifications unless I choose the option to delete him.  What does this mean?

It means that I hope you have another copy of him in a backup. I'm pretty sure that red means he has no character data, and blue is for unlinked... The easiest way to fix No Character data is to locate his character number from the sim browser, then copy the file with that name from the backup to your normal game.