The reason is most likely that one or more of your access requirements have been expired. Have a look at your access requirement page (follow ☞ this link) to see the details. Note that some requirements are assessed by PHS administrators and may take up to 2 business days to be processed.
There are two restrictions for downloading the dataset: (1) data size restriction, and (2) target IP address restriction.
By default, the maximum data size is 1 GB. You can ask for a size-increase by clicking the "Apply for exception" button. State your reasons for the increase in the "Comments" section before submitting.
To solve the target IP address restriction, please contact the admins in the Slack #access-admin channel (☞ see how)