关于武安河一书中的例子，调试出现的错误

我在按照书上说的调试程序的时候出现下面的错误，不明白是什么意思，我刚刚开始学，请大家指教
--------------------Configuration: Regsample - Win32 Checked--------------------
Linking...
Regsample.obj : error LNK2001: unresolved external symbol "struct _UNICODE_STRING  SampleRegistryPath" (?SampleRegistryPath@@3U_UNICODE_STRING@@A)
RegsampleDevice.obj : error LNK2001: unresolved external symbol "struct _UNICODE_STRING  SampleRegistryPath" (?SampleRegistryPath@@3U_UNICODE_STRING@@A)
.\objchk\i386\Regsample.sys : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.

Regsample.sys - 3 error(s), 0 warning(s)