Your IMAP server wants to aler you to the following: Invalid credentials (failure)

Your IMAP server wants to aler you to the following: Invalid credentials (failure)

Hi,
This issue being occuring all the time to our outlook 2010 but we do not have any issue with K-9 mail client.
We do not have e-mail access about 24 hours. Please let us know what is wrong with our end.
Thank you.