The error you posted says you aren't authenticating to the \\PC1\VALIDSHARE with a valid username and password.
Maybe this will help you? You didn't say what OS(s) these 2 systems are running... hmmm If it's a flavor of Windoze why not run a straight bat file starting with a NET USE command? That will let you authenticate to the remote system with a username and password, then map a drive. Then you can run or call or whatever remote bat files you want as you please?
Here's a link to how to use Net Services: http://www.microsoft.com/windowsxp/home/using/productdoc/en/default.asp?url=/WINDOWSXP/home/using/productdoc/en/net_use.asp
