Critical bars Display before Baseline

Member for

16 years 3 months

you must have an end date either on the last activity or project must finish by adte 

Member for

7 years

I have selected the Longest path option but not given the project finish date. Then why it shows some activites in red bar

Member for

16 years 3 months

that depends on how you have your critical path defined it can be zero days total float or longest path

if you have it set to zero days. If you do not set a project must finish by date then the late dates will match the early dates and the float will ALWAYS be zero