conection o imap server failed

[macaringue]

someone memajude porfavor, users on my network not conceguem access roundcube, upon login, got this error "Connection to IMAP server failed" already tried to read most of the articles but I did not have an exact answer on how to solve this problem, will be that one can help me! ai this the image of the error:

http://www.mediafire.com/?w7bxwnfe8tc61c8

aou new in matters of roundcube and iredmail,

thanked everyone who could help