Hi,
Which release/EHP do you use?
For CRM 7.0 EHP2, check if you have implemented note 1889684 or corresponding support package, then SAP note 1955710 might help to resolve the issue.
KBA 1981923 summarizes relevant notes for different browser versions.
If you are on CRM 7.0 EHP3, SP03, you might use the new broadcast messaging component for IC Manager CRMCMP_IC_BM. It supports the same features as the former broadcast messaging
function. In addition, several improvements are available, such as enhanced browser support and the option to select multiple users when creating distribution lists (SAP Note 1931727)
Andrei Vishnevsky summarized his experiences in his blog. New UI component for Broadcast Messages.
Best Regards,
Sigrid