P3 to P3ec 3.5.1 conversion - errors

I tried to convert the project from P3 to P3ec. but to my disappointment, after rescheduling in p3ec it is showing me -ve total float. but the same schedule in p3 does not have any -ve float. i checked calendars, data date, duration types, advanced scheduling options(tried all different options, even lag calendars). everything seems ok. but still it shows -ve total float.

my project has must finish date, which i used in scheduling option too.

am i missing on something? please help.

Thank you in advance.