I can't make sense of this either. Using two empty directories as a test ground:

C:\test\junk>dir /w a b
 Volume in drive C has no label.
 Volume Serial Number is BCCA-B4CC

 Directory of C:\test\junk\a

[.]  [..]
               0 File(s)              0 bytes

 Directory of C:\test\junk\b

[.]  [..]
               0 File(s)              0 bytes
               2 Dir(s)  15,859,965,952 bytes free
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and a simple makefile:

C:\test\junk>type makefile
all:
    xcopy /f /r /i /e /d a\*.* b\*.*
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You can see that xcopy doesn't consider it an error to copy no files with the specified set of arguments, and nmake reports no error:

C:\test\junk>nmake all

Microsoft (R) Program Maintenance Utility Version 7.00.9466
Copyright (C) Microsoft Corporation.  All rights reserved.

        xcopy /f /r /i /e /d a\*.* b\*.*
0 File(s) copied
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You can reproduce the OP error message by (1 of several ways) adding an unknown switch to the xcopy command:

C:\test\junk>nmake all

Microsoft (R) Program Maintenance Utility Version 7.00.9466
Copyright (C) Microsoft Corporation.  All rights reserved.

        xcopy /f /r /i /e /d /b a\*.* b\*.*
Invalid switch - /b
NMAKE : fatal error U1077: 'xcopy' : return code '0x4'
Stop.
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But if that were the problem here, a) we'd see the bad command; b) see the error message identifying it.

But neither of the commands the OP has posted have syntax errors, and regardless of whether there is some other error that is causing there to be no files, the xcopy commands posted are correctly formatted and do not consider the absence of files to copy an error.

I think we have a case of the OP showing us what he thinks we need to see, and missing.