Generally the Store reports are fairly memory hungry. If you have your memory limit very low, try raising it to at least 128mb (256mb or 512mb is preferable - on todays servers memory is cheap).
Another problem people often run into with the reports page is to do with EE's secure forms feature. If you have secure forms enabled, then using the browser back button will not work correctly in your control panel. If you generate a report, then click back, then try to generate another report, you will get an error, or be redirected back to the CP home page. The best solution to this is simply to disable EE's secure forms feature under Admin > Security & Privacy > Security & Sessions > "Process form data in Secure Mode?".