Failed to create listen socket on port 21

Trying to set up an FTP server, Filezilla gave the following error message

Failed to create listen socket on port 21
Failed to create a listen socket on any of the specified ports. Server is not online!

From command prompt run:

netstat -abn > c:\test.txt

In the resulting text file look for a line for 0.0.0.0:21. I found that it was being used by the process inetinfo.exe which is part of IIS. Going to "Services" found FTP Publishing Service was running so disabled and restarted Filezilla FTP server.

Remove NULL values from SQL data result in Excel

If you want to plot a numerical data set that's come from an SQL query, you want to remove the NULL values so they plot as gaps in the series rather than Excel connecting the line between data points...

Select the column.
Press F5 to bring up the "Go To" dialog.
Select "Special..."
Select Constants and then uncheck everything except "Text".
OK twice and then press delete and all your NULLs are gone.