When you are talking about type 1 errors you are looking at a statistical term that means that after running a statistical analysis you have rejected a null hypothesis (the hypothesis that states there is no change) when the hypothesis is actually true. What this means is that in rejecting the null hypothesis (there is no change) you have accepted the alternative hypothesis which means that there is change, when in fact the null hypothesis is correct and there was no statistically significant change within the data that was tested.  This type of error typically occurs in a one-tailed t-test.