you can only use %0\..\ if you use it in a batch file that is started on the netlogon share.

Explanation courtesy of TechNet
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Basically %0 is the current file along with its path (absolute or relative (UNC) path). The \..\ will back you off of a file, the same way that it backs you down a directory tree.
So if I read Ben's scenario correctly...
during logon having :
\\ADomainController\NETLOGON\users\Logon.bat

running the command:
Call %0\..\ThatFile.bat

will be translated to:
Call \\ADomainController\NETLOGON\users\Logon.bat\..\ThatFile.bat

which is the same as running the command:
Call \\ADomainController\NETLOGON\users\ThatFile.bat
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