Copying Files Across Server Using Filesystem Object

I am trying to copy files across servers

I can successfully copy file from server1 to server4
but am not able to copy file from server2 to server4

If I use the code to check for file on server 4
ie
If Fileexists(server4filename) then
response.write("File exists")
else
response.write("File Does not exist")
end if
If I run this code from server1 I get file exists

But if I run the same code from server2 I get file does not exist.

I am logged on as the same user.

Could anyone PLEASE let me know what is the difference on both the servers ie. server 2 and server1.