Failed to Compute Remaining Estimate for Sprint Start with Planning and Worklog on the Same Day

We have upgraded today from GreenHopper 5.1 to the latest version 5.2. When we look up the chart board as a "Hour Burndown Chart" for a lot of versions we get only the red guide line, however, the first version shows all lines. This is particularly awkward as we use the "Required daily burndown rate" to adapt our release plans. The chart was fine before the upgrade.

In the log fine we receive the following message for three issues of the last release that displays okay:

2010-08-18 12:12:26,785 http-8443-9 WARN goeckeler 732x237x1 zj1xhv 10.0.0.15,0:0:0:0:0:0:0:1 /secure/ChartBoard.jspa [greenhopper.service.charts.DefaultHour
BurndownChartService] Failed to compute remaining estimate for sprint start with planning and work log on the same day: VSP-409, 2010-06-30T00:00:00.000+02:0
0

We cannot find any details in the online documentation for this issue, nor does any editing on the issues change anything. The sprints look fine, all dates are set and make sense, Still the error message is displayed.