Each plan has a limit on how many reports can exist in the account at the same time. Once you hit that limit, creating a new report is blocked; existing reports remain available for editing.

To free up space, delete a report you no longer use. Turning off the link doesn't free up the limit, because the report still exists. Another option is to open My Subscription and compare the current plan limits. If an extra package is available for your account, it appears in the limit notice itself.