Do not know is intentional or unintentional, objectarx of all documents, incredibly no cacuilinetypecombobox,
And actually this is there. Located in \inc\acuicombobox.h
There is no such type in the wizard that adds the variable.
Now let's fix this feature.
Open C:\Program Files\autodesk\objectarx Wizards for AutoCAD 2012\arxmemvariablewiz\html\1033
or C:\Program Files (x86) \autodesk\objectarx Wizards for AutoCAD 2012\arxmemvariablewiz\html\1033
Open it
Find to Cacuicolorcombobox
<type name= "Cacuicolorcombobox" header= "" class= "Controlclass" app= "Arxmfc" type= "COMBOBOX" cons= "no"/>
Copy this line in the back to modify Cacuicolorcombobox to Cacuilinetypecombobox
<type name= "Cacuilinetypecombobox" header= "" class= "Controlclass" app= "Arxmfc" type= "COMBOBOX" cons= "no"/>
You can add this type once you've saved it.
Objectarx add linetype drop-down combo box space Cacuilinetypecombobox