Weird notepad error "Common Dialog error (0x3002)"

I was writing an Ant script that creates a simple ascii report and then opens it in Notepad.  I had the following in my Ant script:

<property name="report.file" value="${basedir}/Report-${timestamp}.txt"/>

...
<exec spawn="true" executable="notepad.exe">        

    <param line="${report.file}"/>
</exec>

     

After notepad.exe runs and shows the report, I tried to do a File > Save As, and got this error dialog:

I googled around for it, and all I was finding was people saying to reinstall this and that.  I started out fresh by doing a Start > Run > notepad.exe, and Save As worked just fine, so I figured it had to be something about the way I was launching it from Ant.

It turns out that ${basedir} evaluated to the full path of my project's basedir, with backslashes (\).  I was then appending a forward slash (/) and my file name.  Apparently this confused notepad when it tried to open the Save As dialog.

I fixed it by using the built-in ${file.separator} property that Ant inherits from Java, so my path now only contains backslashes.  My file name property now looks like this:

<property name="report.file" value="${basedir}${file.separator}Report-${timestamp}.txt"/>

This was on Windows XP SP3.