As you can read from psexec help
-c: Copy the specified program to the remote system for execution. If you omit this option, the application should be in the system path on the remote system.
So, your xml file has been copied to the remote sys / USER: [username] username] and executed, this gives you an error.
If your xml is part of an application that you must run on a remote computer, one of them compresses the application with all the necessary files in a self-extracting EXE, which launches the main command upon extraction.
If you just need to copy the file, why not use a simple script that displays the remote folder and then copy the file? Sort of:
NET USE \\computername\sharename password /USER:[domainname\]username xcopy ..... NET USE \\computername\sharename /DELETE
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