If you change the system date of Sharepoint Portal Server from
current date to some back date then the Sharepoint Portal Site does
not functiona properly and gives the followig errors:

Announcement Web part:
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Script Execution Error: Invalid query.


Qucik Links Web part:
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Script Execution Error: Invalid query.


If you change the system date of Sharepoint Portal Server from
current date to some future date then the Sharepoint Portal Site does
not functiona properly and gives the followig errors:

Search, Catgeories, Subscription, Document Library and Management
Dashboards gives the following error:
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Dashboard Error
An unexpected error occurred.
An error occurred while accessing the dashboard. This error may be
caused by the proxy server settings for the dashboard. Contact your
server administrator. If you are a server administrator, configure
the proxy server settings by using the proxycfg utility. Consult the
product documentation and the readme for more information about
configuring the proxy server settings. Important: You must configure
the proxy server settings for the dashboard even if you are not using
a proxy server. (1)