I have been having a similar problem for the past few weeks. My drobo is set to remount as Read Only when disk errors are encountered.
If I run fsck.ext3, then a bunch of errors are found, and need to be manually corrected. Once I do this, the drobo works find for another 3 to 5 days, then gets another disk error, and I need to repeat the process again.
Not sure why the file system is becoming corrupted though. The drobo has not been turned off, and I can not see anything related in syslog or dmesg.
This may the the cause of your system turning to RO.
Anyone have any ideas why the file system suffers corruption on such a regular basis?