Alerts and URL Sequence reports

I am using Free Edition of Applications Manager 6 build 6056 and whenever I choose bookmark 'Alerts' I can see the following information about an error:

"Exception inwebclient/common/jsp/TabComponent.jsp] null
Description
Click Here to go back"

I use Applications Manager to monitor availability of www websites by means of URL Sequence. When I want to prepare an availability report I choose bookmark 'Reports' -> Web Services -> URL Sequence -> Availability of Web Services.
The reports from the current day are correct, but if i choose "yesterday" or "this week" I can see on the display the following message:

"No Data available to generate Reports for the specified time period and limit of reports."

When I choose "last 7 days" and other periods, I can see only the history from the current day!
I was cleaning up the database by means of reinitialize.bat file, I activated repairDB.bat but it didn't help. The history of availability is all the time incorrect, although Applications Manager works constantly, without any breaks for the last few days.
The errors are displayed on different computers with systems Windows XP SP2 Home and Professional Edition (Polish version). I'm mostly interested in this history of availability. What should I do to make the history of availability correct?