showing error following error in soapui open source for generating report.

Below is My Code for build.xml:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!-- WARNING: Exclipse auto generated file.
Any modifications will be overwritten.
To include a user specific buildfile here, simply create one in the same
directory with the processing instruction <?eclipse.ant.import?>
as the first entry and export the buildfile again. -->

<project basedir="." default="testreport" name="REST-Proxibid-Project-1-soapui-project">

<target name="soapUI">
<exec dir="." executable="C:\Program Files\SmartBear\SoapUI-5.4.0\bin>testrunner.bat">
<arg line="-r -j -o -f 'E:\Soapui_Projects\ProxibidProject' -sTestSuite-Proxibid 'E:\Soapui_Projects\ProxibidProject\REST-Proxibid-Project-1-soapui-project.xml'"></arg>
</exec>
</target>

<target name="testreport" depends="soapUI">
<junitreport todir="E:\Soapui_Projects\ProxibidProject">
<fileset dir="E:\Soapui_Projects\ProxibidProject">
<include name="TEST-*.xml"/>
</fileset>
<report todir="E:\Soapui_Projects\ProxibidProject\HTMLReport">
</report>
</junitreport>
</target>

</project>

below is the error showing:

Buildfile: build.xml does not exist!
Build failed

but a file is already located at "E:\Soapui_Projects\ProxibidProject" location.