"Disk is full writing to overflow file"

["Jon P" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender "xywrite4" for DMARC)]

Running XY4 in VdosPlusMac on a Macbook Air,  I'm getting the "Disk is full writing to overflow file" warning when I open a longish text  file--127kb in this case. 

XY4 doesn't crash but the red-backgrounded warning looks scary.

The default drive line in Startup.int is

BX DEFAULT DR=C:\vdosdisk\XY Q2;*;

That folder, Vdosdisk\XY,  is 161MB at the moment. I deleted about 50MB of stray files--much more than 127kb--but I'm still getting the warning. It doesn't pop up on shorter files, only lengthy transcripts like that one.

Any way to stop triggering the overflow warning? Obviously there's plenty of space on the hard drive.

Jon Pareles