This is a known issue on German OS. This has been documented in AX release notes - http://kb2.adobe.com/cps/877/cpsid_87775.html (issue#2734285)
As a workaround, you can try the following:
1. Go to Control Panel->Regional and Language Options on XP
2. Click Customize button in 'Standards and formats"
3. Change the Decimal symbol from , (comma) to . (dot) and click OK
Now try adding comments to the review file. That should help.