DerrenGill & Joel,
Could you please edit the reindexdata.bat found under
\ManageEngine\ServiceDesk\bin and find the following line,
JAVA=.\..\jre\bin\java
update it to the absolute location of the installation like,
JAVA=C:\ManageEngine\ServiceDesk\jre\bin\java
Save the file, run again and check.
Jai Anand K