.hbu files only contain the respondent IDs and part-worth utilities. To run counting, you need the raw data within SMRT (what the respondent's saw in each choice task and their answers).
To do that, you need to import the .CHO file into SMRT. Within SMRT, click File + Import, then browse to your .CHO file.
Academic lab systems are limited to 250 respondents, so it's possible you are currently using an Academic Lab license for SMRT, but trying to analyze a project with more than 250 records. If you believe you have a professional version of SMRT rather than an academic license, please contact support at sawtooth software dot com via email or call 801/477/4700 and ask for our tech support folks.