Visio Web Access: Unable to retrieve data from the server. The web request failed.

I have a multi-server farm with Visio services configured. However when adding the simplest of vsdx files to the Visio Web Access webpart, I get the following error - "Unable to retrieve data from the server. The web request failed." The Details only show - {"ZoomValues":[40,60,80,120]}.

I am unable to find anything in the ULS logs. Infact turning on verbose logging on Visio services showed that the document was successfully retrieved any such but no errors. Nothing incriminating in Wireshark traffic or the Developer Dashboard Based on other posts, I have tried the following -

1. Re-installed Visio graphics services.
2. Re-populated the unattended service account credentials (although there are no external connection in my simple vsdx file)
3. Ensured that the app pool account for Visio has access to the Visio cache folder
4. Ensured that the app pool account for Visio has rights on the content database that has the site collection. I even promoted it to sysadmin with no difference in outcome.
5. Ensured Mime-type for vsdx exists in IIS

I know nothing is wrong with the file because the same works on another single server SharePoint farm that is at the same build level. Same file as vdw works fine. 

Ideas anyone?? Its been 2 days and I am still working on this without a solution.

Thanks in advance,
Jake.