Creating LAG or AE interface in Mist , in Virtual Chassis might result in error AE index must be unique across port profiles

This Article explains step by step procedure to create a LAG or AE interface , forming two different ports in each member id of the virtual chassis 

1) This example shows port , 10 , mge-0/0/10 and ge-1/0/10

First we will click in lead port which will be mge-0/0/10 , then we will form the aggregate from "modify port configuration"

Once there , you can click upon mge-0/0/10 and form the ae , in this scneario I will use AE id 0 ,

Once selecting the ID of AE, to select the port ge-1/0/10 , do not click directly in the backup member , because doing so , will generate this error , AE index must be unique across port profiles

this is an example of how this should not be done:

If we do that , we will cause the error above and AE will not form cause UI will not let you proceed.

2) Instead we will use the box available under the first port we selected which was mge-0/0/10 , please see.. We will click upon port mge-0/0/10 , and click in modify port configuration ,

Once we do this , we can select linecard mode and then select the port ge-1/0/10 ,

Now both ports will be saved , properly as AE0 ...

Using the check box , you can select more ports if necessary