linux - errror when trying to run rds cli commands -

i have following error when trying run rds cli command, have looked , cannot find related describes why getting error:

rds rds-describe-db-instances rds-describe-db-instances:  refused: signature expired: 20160721t013819z earlier  20160721t151824z (20160721t153324z - 15 min.) 

i trying extract logs rds instance, in past able extract logs successfully, credentials have not changed.

any idea why getting issue?