Referring back to the previous page, here we shall now take a look at the log information, to help us in tracing errors, at the very point that they were created; But as it is usual that more error information is captured to the log, than is displayed in Tableau, this can often help in identifying the most likely cause of the error such as: a change in the expected data-type, or the table or column definition being different from that which Tableau was expecting, or that incorrect login credentials were supplied because maybe you have changed your password etc.

For this type of investigation you will need as a minimum:

Given their size, both in row count, but also row length, working with the logs is soo much more easier when opened in a source code editor rather than the Windows Notepad, just be sure that your editor can open and refresh actively in-use files.
Though there are plenty of free and proprietary source-code editors available, my favourite is Notepad++ which you can get from here, based on its size, minimal resource consumption, great feature list, language detection and support, and that it can be ran from a portable exe, so no install necessary