After opening a DGN file AECOsim Building Designer will crash with an exception error.
If the workspace and dataset is pointing to a correct location and there is no configuration issue, then this error may be related to one of *.rul files in the dataset.
If there is still some problem, then please create a Service Request along with the list of all relevant details so that Bentley support can provide an in-depth analysis for possible solution or workarounds.