When validating, the following error message is displayed:
"Object reference not set to an instance of an object"
This is a generic error that data that is typically a result of data that is missing or outside of an acceptable range.
First, try compacting the database. In CONNECT Edition, go to File > Database Utilities > Compact Database. In V8i, go to Tools > Database Utilities > Compact Database. Once you select the database file, choose the option to purge the model to save space.
For one instance of this, a catch basin's gutter shape was set to <None>. Assigning this attribute resolved the issue.