vChart "404 Category not found" error on save

I am using vChart 1.4.0 on Joomla 3.4.8 and an unusual error has started to occur.

When editing any chart, attempting to "Save", "Save & Close" or "Cancel" returns a "404 Category not found" error page.changes are not saved.

We currently cannot edit any of our charts.

Any help would be greatly appreciated.

Hello,
Your subscription has been expired, Please renew it to continue receiving free upgrades and support.

Hi, I've renewed my subscription. Appreciate your help.

Hi,
Please upgrade with the latest version of vChart. And do not forget to take backup of your website before upgradation. If you still find some issues after upgradation, Please share your backend & FTP login credentials via Contact us form, We'll look into it.