I have an iMac with a 2.7 GHz Intel Core i5 with 8 GB of DDR3 RAM. I am running El Capitan version 10.11.3.
On a daily basis I keep a log file using Excel for Mac 2011 version 14.6.0. This particular log file is a whopping (sic) 274K in size. It has no links (internal or external) and no imbedded images or other complexities - it's just a simple spreadsheet with 6 columns and 4492 rows of text data. Today when I added my entry and tried to use Save As back to the same file name, as I do everyday, I got an error message saying "not enough memory" followed by a "file not saved" message.
First, I shut down all open applications except Excel. Still got error.
Second, I tried saving to one of my backup external hard drives. Still got error.
Third, I did a complete computer shut down, restart and opened only Excel. Still got error.
Fourth, I used the backup on Time Machine to retrieve yesterday's log file, restored the current file with yesterday's and tried a save. Still got error.
Fifth, I tried saving another recent Excel file (not the log file) and it saved without error
Sixth, as I write this I get an error pop-up from Excel saying "not enough memory" even though I'm not editing or trying to save anything with Excel. Note the log file is open.