Bamboo has too many open files. This is often due to indexing fragmentation.
To solve this issue shut down Bamboo and clear the index directory (located at /index).
After restarting bamboo you will need to run a full reindex (See 'Indexing' in the Administration section of Bamboo)
If you still are experiencing problems please contact Atlassian Support at https://support.atlassian.com/
Eric Pierce: User Summary