When creating letters, there are two columns of tick-boxes. The one on the left determines which letters will be created. It is most common to have the invitation to tender (ITT) letter and the document list both checked. You can have as many letters created as you want, assuming they are in the templates folder.
The second column determines which letter is the ITT. Exactly one should be ticked and it should never be the document list.
Note: If a template file is open anywhere, there will be a system lock file as well. This will show in the list of templates with a tilde (~) at the start of the name, however, this is not a template and cannot be created. Ensure that it is not this file which has been selected as the ITT letter.