Gnucash thinks data file is read-only, how to open it for writing?

[Ben Finney]

Howdy all,

How can I convince Gnucash to open my data file for writing?

Recently, Gnucash (v. 2.4.13) failed to open a data file, complaining it
couldn't get a lock. I closed Gnucash to deal with this, couldn't find a
lock file anywhere, and re-opened Gnucash. From that point on, though,
Gnucash doesn't complain, but neither will it allow me to save any
changes to the file.

The file has the correct filesystem permissions to allow me to write it.
I can't find any lock file remaining in the directory. How can I
instruct Gnucash to open the file for writing?

-- 
 \       “A computer once beat me at chess, but it was no match for me |
  `\                                     at kick boxing.” —Emo Philips |
_o__)                                                                  |
Ben Finney