Thanks Godra, it's not quite that or maybe it is, i seems like if i have the value 2,8999 then the data logger see it like this: 2 in the first serie and then 8999 in second serie because the plc show 2,8999 and not 2.8999 so the datalogger works fine because it seperates on commas, so my gues is that if the plc show 2.8999 instead it will fit in too datalogger chart afterwards.
Problem solved, Thanks Godra.
I was windows related.