thee is no such restriction number 25 in Data Modeler. Each physical model maintain its own settings for "generate in DDL" flag. So you need to check "tables" tab for selected tables that will go into DDL.
Subview also can be used as filter for objects - you need to check whether relational model or subview is selected in second combo box in DDL file editor.
And to check about errors in the log file - "View>External log"