This is a known issue with Wacom tablets.
Please follow the below instructions.
- Open the Control Panel and type "tablet" into the search field.
- Select "Pen and Touch" settings from the "Pen Options" tab, select "Press and Hold" and click "Settings...".
- Make sure "Enable press and hold for right-clicking" is unchecked.
- Click OK.
- Select the "Flicks" tab.
- Make sure that "Use flicks to perform common actions quickly and easily" is unchecked.
- Click Apply, and OK.
If you have Windows 7 and the above does not fix your problem you can try the below.
- Open Control Panel.
- Under Devices and Printers click Device Manager.
- Open the section in the tree called Human Interface Devices.
- Right click on Wacom Virtual Hid Driver and choose Disable.