I just started working with this software

I got 8 tasks in and was linking them all serially by typing in the predecessors manually everything was working great until the start date quit changing on the 7th task. 

A yellow calender icon appeared in the first colunm stating 'task has a 'starts no earlier than' date'

I have tried to adjust this every way I can think of to no avail, I modified the properties window, changing the start date options and no matter what I choose they keep going back to 'starts no earlier than' 

I also tried: insert lines, delete lines and try again, restart projectlibre, insert lines above line 7.... 

now the predecessor function is completed unusable in my whole project... even changing tasks that worked before do not update the start date if I change the predecessor and refresh links. 

Anyone else seen this? How can I get this to work???