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The following URL provides the answer and details the reasons<br />
<a href="http://technet2.microsoft.com/WindowsServer/en/library/cfe07b0a-20d1-4b9a-8faa-044e43cbb5921033.mspx?mfr=true" rel="ugc nofollow">http://technet2.microsoft.com/WindowsServer/en/library/cfe07b0a-20d1-4b9a-8faa-044e43cbb5921033.mspx?mfr=true</a><br />
<br />
&quot;You can run Adprep.exe multiple times, but it performs actions only once. For example, Adprep.exe does not adjust access control lists (ACLs) each time you run the command.&quot;<br />

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The following URL provides the answer and details the reasons
http://technet2.microsoft.com/WindowsServer/en/library/cfe07b0a-20d1-4b9a-8faa-044e43cbb5921033.mspx?mfr=true [http://technet2.microsoft.com/WindowsServer/en/library/cfe07b0a-20d1-4b9a-8faa-044e43cbb5921033.mspx?mfr=true]

"You can run Adprep.exe multiple times, but it performs actions only once. For example, Adprep.exe does not adjust access control lists (ACLs) each time you run the command."


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I'm not sure if &nbsp;w2k3 adprep /forestprep has already been run <br />
<br />
runnig it twice, can make any damage &nbsp;or just an error message ?
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I'm not sure if  w2k3 adprep /forestprep has already been run 

runnig it twice, can make any damage  or just an error message ?

run adprep /forestprep twice

Windows Server 2003 was based on Windows XP and was released in four editions: Web, Standard, Enterprise and Datacenter. It also had derivative versions for clusters, storage and Microsoft’s Small Business Server. Important upgrades included integrating Internet Information Services (IIS), improvements to Active Directory (AD) and Group Policy (GP), and the migration to Automated System Recovery (ASR).