error LNK2019: unresolved external symbol fun referenced in function main

I have a project in vc++ which using standerd windows library and source file include file1.h.A method in header file defind as
 
file1.h
 

void _stdcall fun(char * text);

but the plateform was the x86 and vc6.Now I converted the project in vs8.and plateform x64.I also add the file1.lib file in x64 plateform.But when I execute the project the error occure that
 

error LNK2019: unresolved external symbol fun referenced in function main