Consider the following scenario:
- You install a 64-bit version of Windows Vista, Windows 7, or Windows Server 2008 R2.
- You set the time zone to Israel Standard Time. In Windows Vista, this is displayed as (GMT+02:00) Jerusalem. On Windows 7 and Windows Server 2008 R2, this is displayed as (UTC+02:00) Jerusalem.
- You do an in-place upgrade to a 64-bit version of Windows 7 or Windows Server 2008 R2.
After the upgrade, the time zone setting is correctly configured and such features as Dynamic DST continue to work.
After the upgrade, the current time zone cannot be recognized by the GetDynamicTimeZoneInformation() API. Without user intervention to correct this, Dynamic DST is broken and the computer does not adjust for DST on the correct dates in upcoming years. Therefore, the displayed time on affected computers does not match the current local time.
When this problem occurs, users do not receive a notification about the error.
Additional Windows Server 2008 R2 problem
On Windows server 2008 R2 servers, you cannot change the time zone setting, and you receive the following error message:
Your current time zone is not recognized. Please select a valid time zone.
The TimeZoneKeyName registry setting is defined as a 128 WCHAR REG_SZ data type. If the 128th WCHAR in TimeZoneKeyName is not a null terminator, the system upgrade process (Offline.xml) appends a null to the string. This increases its length to 129 WCHARs. Because Windows has a 128 WHCAR buffer in which to store this data, the system does not load the modified string from the registry.
This problem applies to upgrades to 64-bit Windows 7 and Windows Server 2008 R2.
Additional Windows Server 2008 R2 cause
Permissions are missing on non-working servers for the following registry subkey:
HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones and HKLM\System\CurrentControlSet\Control\TimeZoneInformation
On Windows Server 2008 R2 computers, start the Date and Time item in Control Panel or on the Windows task bar. If the message in the clock window indicates that the time zone is unrecognized, click Change time zone, verify the time zone setting, and then press OK. This restores correct values to TimeZoneKeyName.
On Windows 7 clients, verify your time zone selection during the OOBE phase of Setup. This restores the TimeZoneKeyName setting in the registry.
- The Windows operating system uses UTC time internally for time-dependent operations. The displayed time that appears in the Windows task bar or Control Panel item is based on UTC time plus or minus a regional time offset corrected for daylight saving times rules based on the local computers time zone locale.
- This bug does not affect the internal system time used by Windows. It can cause the displayed time to appear incorrect.
- When you correct the time setting in the Date and Time item, first verify that the the correct time zone has been configured. Do this before you make any date or hour changes so that you do not unintentionally configure an incorrect system time.
In some countries, the DST dates differ from year to year and cannot be defined by a single rule. Therefore, Windows includes the Dynamic DST feature that stores per-year rules in the registry. When the year changes, the current time zone information is refreshed by using the correct DST information for that year.
Dynamic DST depends on the following registry value being set to the name of the time zone key where the Dynamic DST data resides (for example, “Israel Standard Time”):
Only time zones that have different rules for different years (Dynamic DST) are affected. This is because the registry value that indicates where these per-year rules are stored is corrupted.
If this value is missing, the time zone information data is not refreshed at the next year changeover period. This causes the previous year’s DST rules to be used to calculate local time.
Immediately after the system version upgrade, display time is not affected by this issue. You will get a notification of an unrecognized time zone if you click the taskbar clock or open the Date and Time item in the Control Panel.
If the time zone is not corrected, future transitions to or from DST could occur at the wrong time. This would cause an incorrect time on the system, or incorrect conversions between system and local time being incorrect.
All time zones are potentially affected, but the main effect is on operating system installations that are configured to use zones that contain Dynamic DST data. The time zones that support Dynamic DST are as follows:
Alaskan Standard Time
Arabic Standard Time
Argentina Standard Time
Atlantic Standard Time
AUS Eastern Standard Time
Cen. Australia Standard Time
Central Brazilian Standard Time
Central Standard Time
E. South America Standard Time
Eastern Standard Time
Egypt Standard Time
Greenland Standard Time
Iran Standard Time
Israel Standard Time
Mauritius Standard Time
Montevideo Standard Time
Morocco Standard Time
Mountain Standard Time
New Zealand Standard Time
Newfoundland Standard Time
Pacific SA Standard Time
Pacific Standard Time
Pakistan Standard Time
Paraguay Standard Time
Tasmania Standard Time
Venezuela Standard Time
W. Australia Standard Time
The reason that the impact in this case is greater is that the DST data for the time zone may not be updated to reflect the rules that should be in force for the given year. This may cause a transition to or from DST to occur at the incorrect time in the given time zone. This is not an issue if Dynamic DST is not present in the time zone. However, the corrupted registry data causes any call to GetDynamicTimeZoneInformation() to fail, regardless of whether the time zone supports dynamic DST.