I recently had a problem with my usually excellent Dropbox. Particular files, such as KeepassX files (*.kdb), BibTeX files (*.bib), and MS Office files (*.xls, *.doc) would not upload from my Ubuntu machine at home. On my other three machines at work running Ubuntu, Windows, and Mac OS X, everything runs smoothly.

At first, I thought the problem was related to encryption (the *.kdb files), however, the MS Office files were not encrypted. Then I discovered that my Mendeley desktop application would not download (sync) my files and it reported that this could be due to me sitting behind a proxy or firewall. This put me on the right track. I had no firewall running on my Ubuntu at home but perhaps I had messed up something in my wireless ADSL router?

I went into the settings but could not find anything obvious. I changed a few things and rebooted both the PC and the router, but to no avail.

I decided that there was still a possibility that I had screwed up something in the router, although I was unable to pinpoint what. So I reset the router to its factory settings, and voila! Both Mendeley and Dropbox now works seamlessly!

It is unfortunate that I do not know the exact reason for the problem. I have done some port forwarding for other applications on particular ports. Perhaps Mendeley and Dropbox have been affected by this, although I cannot see why opening ports should be a problem.

More likely is the fact that the router comes with a built-in firewall that may be blocking some of outgoing and incoming connections made by Dropbox and Mendeley.

Finally, I noticed that UPnP (Universal Plug ‘n Play) was disabled in the router after the factory reset.

I am not going to be bothered to experiment to find out exactly which setting caused the problem but will update this post if the problem returns.

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