FYI… I was able to resolve this issue by modifying the upstream and downstream cross sections associated with each of the “problem culverts”. Each of these cross sections included a horizontal segment at each end. I realized these segments were the offenders because the IB calculations was crashing at the the top of each problem cross section. By adding 0.01 ft elevation to the first and last point of each cross section and eliminating the horizontal segments, the preprocessor was able to complete without issue.