Hi,
This is not an error message, a warning message. This warning is merely a (friendly) reminder to the user that he/she should be careful when using the Floor load, Area load function or non-linear analysis when the SET Z UP command is used. The warning does not necessarily mean that anything is wrong with the loads, but just that the user should be aware that in such instances it is necessary to avoid Floor load functions. If your model does not have the issues mentioned in the notes, you do not need to worry about the warning.
It is better to use the PERFORM ROTATION command instead of SET Z UP command. In this case, you can create the model in STAAD.Pro with vertical Y axis and use the command PERFORM ROTATION X -90 to modify the model to the same condition(using SET Z UP). You need to specify the PERFORM ROTATION X -90 command after all the member incidences have been defined.
