Redeploying FMS 16 (via the Edit Deployment) did not work for me, had to do a complete uninstall and re-install of FMS 16. Then reinstall MS. Specifically the following was done in this order.
1 - Reboot - still did not respond giving 959.
2 - Try Redeploy - still did not respond giving 959.
3 - Reboot after Redeploy - still did not respond to giving 959.
4 - Uninstall MS, reboot then redeploy, - still did not respond to giving 959.
5 - Uninstall FMS, reboot, then re-install FMS and then MS - success, no more 959!
To be clear this was not an MS specific issue, as it was the FileMaker XML engine basically broke randomly (after months of working fine), but thought it would be useful to post here as this was one of the top Google hits for the 959 error.