This is a little weird. I got an ant build working fine but I had to define a
property for the build to succeed. As soon as I did the log showed that the path
to ant was now proving to be a problem.

In the first case, this is the command that was executed:

cmd.exe /C "C:\Program Files\eclipse\plugins\org.apache.ant_1.6.5\bin\ant.bat"
-file build.xml && exit %%ERRORLEVEL%%

In the second case this was the command:

cmd.exe /C "C:\Program Files\eclipse\plugins\org.apache.ant_1.6.5\bin\ant.bat"
-file build.xml "-DTOMCAT_HOME=C:\Tomcat\Tomcat 5.5" && exit %%ERRORLEVEL%%

The only difference is the addition of "-DTOMCAT_HOME=C:\Tomcat\Tomcat 5.5", but
this is the error I get:

'C:\Program' is not recognized as an internal or external command,
operable program or batch file.

Note that without the property definition I don't get this error.