Oracle has its own built-in error codes, which can be found online or via the "oerr" command.
[amcom@amcom1 ~]$ oerr ora 1400
ORA-01400: cannot insert NULL into (string)
Cause: An attempt was made to insert a NULL into the column "USER"."TABLE"."COLUMN".
Action: Retry the operation with a value other than NULL.
In most databases, a column in a table can be set up to be either null or not null. If nulls are allowed, then no data is required to be passed to that column. If it's a not null column, then the column cannot be null. In Smart Suite, this can occur wherever data is being inserted.
For example, in an hl7 interface, this can occur if no data is passed to one of the two required fields in the patient table.