QT1: I am getting "[AnyDAC][DatS]-15. Duplicate row found on unique index" when navigating in TADTable ? What that means ? 

A: In most cases that means, that the DB sort order and the client sort order differ. That may lead to endless loops or [AnyDAC][DatS]-15 error. To resolve the issue, setup the FormatOptions.SortLocale and SortOptions properties, so that the client sort order will match to the DB sort order. 

QT2: When navigating through TADTable records my application is hanging. What is wrong ? 

A: See QT1.