[OSM-newbies] Unable to upload to OSM from JOSM

[Bob Hawkins]

Twice today, and for the first time since I have been working with JOSM, I have been unable to upload the map data I have plotted.  Following my clicking 'Upload to OSM...', I am presented with the dialog 'Uploading data' and the progress bar headed 'Preparing OSM data...'.  After some time, a Message box pops up stating, 'Cannot read numeric value from response'.  Meanwhile, the 'Uploading data' dialog progress bar heading has changed to 'Opening changeset...'.  This disappears when I close the Message box.
Although I have not created a tremendous amount of data in this session, I am reluctant to lose it.  What should I do?  I see File>Save and File>Save As... but JOSM Help provides no further explanation.  Am I able to save my data in some format or other and then open it in a future session of JOSM and merge it with the data already held on the server?  I should appreciate users' advice and assistance.
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