How do I export Outlook for Mac datat file to .olm file?

I need to export Outlook for mac data file to .olm file format, but there is a situation which disables me to export or open the .olm file and outlook 2011 for mac gives errors as I do so. I contacted some professionals but their advice was a dead end. They asked me to re-build the outlook for mac identity but it was of no use. I am still not able to export the Outlook for mac (.olm) data file.