DvSum rule execution allows you to see the potential bad records in your data source. It also saves these exceptions in to an excel file which can be downloaded from Analysis tab on the rule detail page.
The "Export" button will download an excel file of exceptions for this rule but this button is only enabled when there are exceptions in the run result. If the executed rule passes, which means there are no bad records identified in your data source then there will not be any report to download. Hence, the Analysis tab will be disabled.