'Illegal directional connection'error in Quartus 8.0

I don't know the port type of data_out, but this most likely can't work. You'll need a tristate driver interface.

port map
(data_in=>data,
data_out=>data_o);
data <= data_o when (enable_condition) else (others => 'z');

P.S.: If data_out is of the output type, and you simply want to override the inout character of data (permanently enable the output buffer), there may be technical problem of the Quartus compiler. In this case, try to insert a dummy signal between data_out and data.