The "Not enough quota.." exception appears to be caused by the operating system virtual memory management.

 

Some machines have virtual memory settings set to "System managed size".  By explicitly setting the minimum and maximum virtual memory sizes, the issue went away and general performance of Navigator improved.  Also, the degradation of performance over time seemed to disappear.  Another setting to change was to set the "Adjust for best performance of" to "Programs" (rather than Background services).  Here are the steps used to set the virtual memory settings:

 

On the machine:

  1. Control Panel -> System -> Advanced system settings (on the left side) -> Advanced Tab -> Performance 
  2. Set Adjust for best performance of to Programs
  3. Click the Change button under Virtual Memory:
  5. Select the Drive and then select Custom Size.  Set Initial Size (MB) and Maximum Size (MB)
    1. Initial Size (MB) and Maximum Size (MB) settings depend on the machine's RAM.
    2. Example:
      1. Initial Size (MB) 6144 
      2. Maximum Size (MB) to 12288 
  6. Click the Set button.  
  7. Then OK out of all dialogs

For more information see these articles:

https://docs.microsoft.com/en-us/previous-versions/ms820778(v=msdn.10)?redirectedfrom=MSDN
https://stackoverflow.com/questions/20964360/not-enough-quota-is-available-to-process-this-command-wpf