It is probably because it is over an association.

First set a dataview with the needed association, put the date picker in that dataview.

Some thoughts; 

1. Besides R/W access to the attribute, does the user have read/write access to the consumed association
2. Are you really consuming the same association to the same entity/object?
3. Is the date a stored value? (Calculated won't be editable)
4. Are these dates in the same page? if not, check existens of the nested object

Regarding this comment " FYI: those over dataview use the same association but i need to get it's source with difference tables" What do you mean with tables? tables as layout/structure of page or tables as in database tables?

It could be several things I think:

- the most abvious: do you have sufficient Write rights on the attribute?

- Is your dataview (and all of its parent dataviews) set to Editable: Yes

- Does the object you are trying to edit actually exists? You can test this if by checking if you can see the values of other attributes of the object in that same dataview

Thanks for  your reply. I have full read & write access rights & my dataviews is set to editable. In my case, i just want to get data from date picker. I'm not edit or create anything.

As @Tim suggestion. I wish it was but in my screenshot date a & date b are not disabled but date c is disabled. I did check all as @Bart suggested but it's not working. FYI: those over dataview use the same association but i need to get it's source with difference tables

Hi @Rene van Hofwegen, for your questions:

 1. User did have r/w access to the consumed association

 2. I did consume the same association but with different entity

 3. Yes, it's stored value by default

 4. Yes, these dates are in the same page

In my last comment, i meat entity (tables) in domain model ( Sorry for the wrong information).