It is not easy to give an answer without knowing the version, settings etc. I’m not able to recreate this in our test environments. It would be better if you report a support case so we can help you investigate what is causing this error. Please provide information on how to recreate the issue, the outlook and ifs version and also include log entries from the CRM-panel. You can click Settings in the upper right corner to enable log entries before you try to create the opportunity. If you copy that log to the case it is easier for us to find out what’s wrong.

Not sure if this will help (we have had similar in Apps9) but check Search Domains to see if any are not valid/indexed.  

select index_name,index_type,status,domidx_status,domidx_opstatus from user_indexes where index_type = 'DOMAIN' and (domidx_status <> 'VALID' or domidx_opstatus <> 'VALID');