New issues can't be ranked. The error message displayed is:

in red or in yellow message.

JIRA Agile cannot execute the rank operation. This board has recently been configured to use the Rank field. The system must be re-indexed before you can rank issues. Ask your administrator to perform a manual re-index.

Cause:
When new issues are created, JIRA Agile fails to assign a new Rank value to issues.

To verify:
Do an issues search <JIRA-BASE-URL>/issues/?jql=order%20by%20created%20desc and add Rank as a column to the list. New issues won't display a Rank value.
If they now do, then they will be able to be ranked now.

Workaround: (on OnDemand create a support request at http://support.atlassian.com )

1. run a rebalance with sysadmin user going to <JIRA-BASE-URL>/rest/greenhopper/1.0/lexorank/balance
2. run a Background reindex.

Notes:
This query can be used in the database to find what issues don't have a Rank:

select  p.pkey, j.issuenum, p.pname from jiraissue j left join project p on p.id = j.project where j.id not in (select "ISSUE_ID" from "AO_60DB71_LEXORANK") order by p.pkey, j.issuenum;