Dimensions won't trim or extend?Why?

Okay so you can trim and extend dimensions in AutoCAD, how cool! But (and
there's always a but) sometimes I can't, beacause _ _ _ _ _ _ .

Please fill in the blanks.

Your prize for getting it right is a joyfull and gracious 'thankyou'.

Thanks
Monty

 

DIMASSOC (2) and dims are not exploded. What else could it be? Thanks for
the reply.

DIMENSION Layer: "0"
Space: Model space
Handle = A0
associative: no
type: horizontal
1st extension defining point: X= 8.5713 Y= 17.7669 Z= 0.0000
2nd extension defining point: X= 32.8418 Y= 17.7669 Z= 0.0000
dimension line defining point: X= 32.8418 Y= 24.0143 Z= 0.0000
default text position: X= 20.7066 Y= 24.0143 Z= 0.0000
default text
dimension style: "Standard"

 

You have to make sure the Definition points of the dimensions
cross-over the same plane as the line(s) that you are
trimming/extending to.

 

That's not mandatory necessary: you can use trim/extend -> Project ->
....

Juergen