Even though one has maintain access to transaction OB52, in QA (TEST) system the SAP system won't allow to open periods or maintain entries.
This issue happens only Client role is set as "TEST". (you can check in transaction SCC4).
One alternative fix for this issue is just change your Client role as "Production" for a minute, open your periods in OB52 and then change back the role to "TEST".
Or else refer to SAP Note 356483 for furhter information.