I baselined a schedule that has around 1,100 activities a couple of months ago and I'm updating it on a bi-weekly basis. When I issued the baseline, my float was zero, in other words, I didn't have negative float. Now, I'm getting big negative floats, especially on ongoing activities that have a 7-day calendar. Why? Can anybody help me on this matter? Thanks in advance.
More information is needed to dismiss the obvious: that your last activity has been scheduled beyond the project's finish constraint date. Or that a task somewhere in the middle has done the same (probably keeping it 0 TF at the end). TF has no dependency on your baseline, so forget using that as the culprit.
I recon you to check the constrains in the activities with negative floats. Next thing you can check is whether the task it resource dependent and you have allocated a resource with different calendar.
It is hard to give precise answer without details but hope above will be helpful.