Sometimes it results impossible to drag the fields of a table in the trash.
Even after closing and reopening the tables and the project and the browser.
It seems to be locked on the leftmost column (as when you reorder your fields up and down).
Does soemeone experience the same behavior ?
I have no work around unless to trash the entire table
or to rename the field for another usage. (assuming that you need another field of the same type !)

Yes couple of times it happened to me too. Logout and restarting browser helped.

In my case this has not fixed the problem.
The very latest release of firefox > 14 delivered with ubuntu 12.04 have some strange behaviors..
as auto-logon between sessions.. etc
I don't know if this bug is not related with or not.
I have no such problems with previous firefox releases.
I have fixed the problem opening the Cook framework on another Windows computer with firefox 10 installed..
where I have removed the unwanted fields

If your browser make confusion of login between 2 different session, it can be a major problem.
Did you tried to sign out all your sessions on this computer, then log in only with one account.

And then try to do this operation.

In case of such issue, can you tell be the JS error ?

OK
... for now I have no longer the problem cause I solved it by other means.
But if it occurs again, I will let you know of course.