I'm trying to run a viewshed analysis. I've already run it once and it worked fine, but wanted to change some parameters and now I keep getting the same error code over and over when I run it. Error code 010067: Error in executing grid expression. Cannot open LAB for LAB. Cannot open point file for LAB. Cannot open INFO file NEW_APT_PTS.SHP.pat (my observer point file). I'm at a loss for what to do. Any ideas?