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'