Can't save file in TextEdit.

[DaveOlden]

First, I'm running MacOS X 10.11.6 on a MacBook Pro (17-inch, Mid 2009).

Problem showed up today.

1. I create a new blank document in TextEdit.
2. I write what I need into the doc, then press ⌘+S to Save.
   
3. I name the file with (in this example) "test save.rtf"
   
4. When I click the <save> button, I get this error message: (I've attached a screenshot)

The file "Untitled 8.rtf" couldn't be opened

[OK]​

I have never seen this error before. It's saying "couldn't be opened" at point of save?

​

 

[chscag]

I'm running Sierra 10.12.3 and just ran a test with TextEdit and was able to save the file first as "test save.txt" and then did the same thing but this time used "save as" and was able to save the file as "test save.rtf". No errors.