The issue occured as no temporary directory ( referenced in the opmn.xml file ) existed on the server that was needed for temporay file creation during the process.
The opmn.xml file had the following entry below for TEMP/TMP environmental variables but no physical location existed on the server. Creating the directory ( as plenty of space on that disk existed ) solved the problem.
<ias-instance id="fmds" name="fmds">
<variable id="TEMP" value="C:\temp"/>
<variable id="TMP" value="C:\temp"/>
After creating the directory c:\temp , when exporting the file the following message appeared
The export you created is ready. Please click the button below to open the exported document to view or save it.
Click to view or save