Real Salt Lake's errors against Colorado were many and frequent, but the sole goal scored was less a tactical failure and more a series of individual mistakes.
Aside from the fairly obvious answer — Real Salt Lake conceded an early goal and couldn't recover — there's something more interesting to be taken from the goal scored. Three things happened, and only one of those could rightly be blamed on Abdoulie Mansally. Nat Borchers allowed Edson Buddle to hold up the ball deep in the box, Schuler slipped, allowing his man through and disrupting the defense, and Mansally left his man to attempt to correct for the individual mistake, giving former RSL man Atiba Harris a clear opportunity.
Why'd it happen?
Does Abdoulie Mansally allow for a weakness in Real Salt Lake's defense? Mansally is obviously an attacking full back, and as such, sides may feel they have good opportunities at RSL's wide left position. This seems fairly obvious, the slightly left-leaning bent of RSL's central defenders corrects for that in some important ways. Although he — and plenty of others — were culpable in that early goal from Colorado, it was because of several individual failures in defending and less because of a systemic tactical failure.
How can it be corrected?
It's difficult to tactically correct for individual errors, save for a defensive strategy that provides more defensive cover in all areas. This is fundamentally in conflict with Jason Kreis's strategy for the side, although certain sorts of players can provide some types of fixes. Take, for example, Jamison Olave, whose ability to recover and prevent an attack was used as a solution to this problem. But without a player like Olave, the defense is often left in a situation where a greater responsibility from everyone is required. Single mistakes are inherently more likely to be punished.