I have in problem when appending data: I need to import those data from Excel in the panel format. The problem is that when I use the command "Append" I get the message "Data frequency does not match" even though I'm appending to the dataset a variable of the same frequency of those that are already inside the dataset.

For example, I start a new session and I first import my first variable using the command "import" and then giving the panel interpretation (stacked time series and then choosing the number of cross section and time units). Then when I want to append a second variable I use the command "append" but even though the second variable has the same frequency of the first one I get the message "Data frequency does not match".