Often when I go to add a field to an SSRS Report, I see #Error when I first try to display the field. The solution is simple, I just forgot to add .Value to the end of the expression for the field.
I normally wouldn't consider something so insignificant to be blog-worthy, but today I spent about a while trying to figure it out before a co-worker reminded me. I'm putting it here so I can find it in the future! Hopefully it will help someone else.
I discovered today that a search for SSRS Report #Error doesn't bring up much that's helpful, I found a few links that mentioned "divide by zero" issues.