This should not happen anymore from Eclipse Indigo or newer and Subclipse version whatever, but it happened to me today using Helios.
Long story short: this message means that you have a conflict somewhere in your project, just check which file(s) is/are marked with the conflict icon, and solve the conflict (right click/team/mark resolved… and pick the action you want to perform). That’s it!
something I did not know 
Thank you! Initially I thought its a SVN access issue but as you mentioned resolving the conflict fixed the issue. I wish SVN displays a little bit more helpful error message.
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yeah, it’s not very helpful, is it? š
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Saved me a ton of time. Thank you!
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happy to help! š
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