Try to upload a file in the "Publish"->"Media Manager" page.
If it shows that there is not enough space for uploading, you can delete files by clicking the "Delete" link next to the files to release more space. Please note that only deleting files that are uploaded in the current month will release space for your monthly limits. Alternatively, you can wait till the beginning of next month when your monthly space will be reset and you're able to upload again. Of course, you can also upgrade your account to a plan which has larger monthly space quota. We now offer unlimited plans for a great value!
If it shows "IO" error when try to upload, please try to upload later for this error is caused by a slow network.
If there are other error notices, please contact us and send us the screenshot of the error page. Our tech team are always ready to help.