The save failed due to lack of memory or disk space.

The message is caused by how Word manages memory, paging, and temporary files during save, not by the total RAM or disk size of the Mac.

When Word saves a large document, it:

• Creates temporary work files.
• Uses additional disk space for paging/virtual memory.
• Replaces the original file with the newly saved version.

If anything in this process fails (temporary file cannot be created, disk/paging area appears full, or an environmental interruption occurs), Word reports errors such as:

• “There is not enough memory or disk space to complete the operation.”
• “Word cannot save or create this file. The disk may be full or write-protected.”
• “There is a serious disk error on file ~Word Work File S{<filename>}.tmp.”

This can happen even on a Mac with large storage and 16 GB RAM, especially with a very large document (179 MB) and long editing history.

To mitigate and work around this:

1. Install the latest Office for Mac updates
   Outdated builds can have save/autosave bugs that affect large files.
   • Open Word (or any Office app).
   • On the Help menu, select Check for Updates.
   • Under How would you like to check for software updates?, select Automatically.
   • Choose how often to check, then select Check for Updates and install all available updates.
2. Reduce memory and paging pressure
   Word save failures are documented when the system paging file grows and consumes available disk space.
   • Quit all applications that are not needed.
   • After closing them, wait a few minutes so the system can reclaim memory and adjust paging/temporary usage.
3. Ensure there is free space on the system drive
   Even with a 2 TB disk, if the system volume (where macOS and Word are installed) is close to full, Word may not be able to create or expand its temporary files.
   • Remove or move files you do not need from the system drive to free space.
   • Focus on freeing space on the volume where the document and Word’s temporary files reside.
4. Try saving to a different location
   If the current folder or volume has issues, saving can fail.
   • Use File > Save As and save to:
     • A different folder on the same drive, or
     • A different drive (external disk or network/OneDrive location), or
     • Another volume with more free space.
5. Be aware of temporary file issues on Mac
   On Office for Mac, save and autosave create temporary files and then replace the original. If something environmental interrupts this (disk error, permissions, or temporary path issues), Word can show “serious disk error”–type messages and fail to save.
   • Keeping Office updated is the primary fix.
   • If problems persist after updating and freeing space, contact Microsoft Support so they can review the specific environment and document.

These steps follow documented behavior where Word’s save process and the system’s paging/temporary storage can cause save failures, even when the machine has ample total RAM and disk capacity.

References:

• You receive an error message or the program stops responding when you save a document in Word
• There is a serious disk error on when attempting to save, copy and paste or create auto recovery files in Office for Mac