Table Multiselect - TypeError: unsupported operand type(s) for +: 'type' and 'unicode'

So I have created a custom doctype named “Dive guide”

“Dive guide” I would like to have it as a table multiselect in inside the Event doctype as a table.

However, when I try to save the doctype “Dive guide” I receive the following server error:

TypeError: unsupported operand type(s) for +: 'type' and 'unicode'

Anyone else is experiencing this ?

Ok so I managed somehow to put the table multiselect - I will trace back my steps and post it here later.

Now however, when viewing the table in the Event doctype, the table multiselect is not visible ( by the way, it cannot be set as list view ) and you also cannot open the table to be able to see the fields of “Dive guide” doctype.

Is this a normal behaviour ?

UPDATE: Somehow it works after receiving multiple server errors.