Total float in decimal peoblem

Edit, User Preferences, Time units.

Primavera does ALL of its calculations in hours. Yes, the rounding to whole days is not useful.

You need to get to the underlaying problem which is the reason that your float is not a whole number is because your TIMES are incorrect and or your remaining durations are in fractions of a day.

if you look a 1 day activity I am certain that you will find a 1 day activity actually spanning 2 days. It shows planning to start on 1 day but is forecasted to finish on the next when it should start AND finish all on the same day.  

To fix this turn on your times by selecting edit users preference then on the Dates then at the bottom select the 12 hours 

also click on the Time Units tab under duration format select 2 decimals.

now go to the project directory make sure that your project is highlighted and select dates and look at your project start date and make sure that the TIME is 8:00 am or the earliest hour in any of your calendars being used.

now look at your data date make sure that TIME is 8:00 am or the earliest hour in any of your calendars being used

now look at your project must finish by date and make sure that the TIME is the 5:00 pm or the latest time in all of your calendars being used.

also look for any milestones or constrained activities change any start TIMES on the constraints to 8:00 am or the earliest hour in any of your calendars being used and change any of the finish milestones constraints being use to  5:00 pm or the latest time in all of your calendars being used.

Also ALL actual start TIMES should be 8:00 am or the earliest hour in any of your calendars being used and any actual finish date TIMES should be 5:00 pm or the latest time in all of your calendars being used.

Lastly look at all of your inprogress activities and make sure that remaining durations are in WHOLE number of days.

This will correct your float issue

thanxx Zoltan

so if i have 1 month in my calender in which the working hours/days is decreased from 8 to 6h/d could this cause the problem because the ativities during this month have a full day hours ???

yes you need to add another calnedar and assign the activities to the correct calendars.