While executing the following code:

        doc = builder.parse(file);

where doc is an instance of org.w3c.dom.Document and builder is an instance of javax.xml.parsers.DocumentBuilder, I'm getting the following exception:

Exception in thread "main" java.net.MalformedURLException: unknown protocol: c
        at java.net.URL.<init>(Unknown Source)
        at java.net.URL.<init>(Unknown Source)
        at java.net.URL.<init>(Unknown Source)
        at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.setupCurrentEntity(Unknown Source)
        at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.startEntity(Unknown Source)
        at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.startDTDEntity(Unknown Source)
        at com.sun.org.apache.xerces.internal.impl.XMLDTDScannerImpl.setInputSource(Unknown Source)
        at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.dispatch(Unknown Source)
        at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.next(Unknown Source)
        at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(Unknown Source)
        at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source)
        at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
        at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
        at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
        at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source)
        at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(Unknown Source)
        at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(Unknown Source)
        at javax.xml.parsers.DocumentBuilder.parse(Unknown Source)
        at com.acme.ItemToThetaValues.createFiles(ItemToThetaValues.java:47)

It's choking on this line of the file:

<!DOCTYPE questestinterop SYSTEM "C:\Program Files\Acme\parsers\acme_full.dtd">

I am not getting this error on my machine, while a user is getting it on his machine. We are both using version 6 of the Sun JRE. This error also occurs when he's uses double backslashes in the path instead of single backslashes and when he uses forward slashes instead of backslashes.

First of all, is the XML correct? Is the path expressed correctly? Second of all, why is this error occurring on one computer but not on another?