Hi maurlind,
I got it, the function that derived the linear fit couldn't handle that large numbers on the x-axis. I edited the VI so that the large number is suctracted for the fit, i.e. the array will now begin at zero time for the fit. It will not affect your plots though, only the algorithm :).
Try it now with the files I provided. The file "pm_mod2_Rawsignal test.vi" should be used with "test3.lvm" (your data). The file "pm_mod3_Rawsignal test.vi" is the same as "pm_mod2_Rawsignal test.vi", but it is arranged to work with the simulated data. The file "test3.lvm" is your data, but the file is slightly edited to work on my system.
Edit "pm_mod3_Rawsignal test.vi" to fit with your acquired signal as you did with the first file you got from me.