Workflow 7.6 WebForm Style Editor Error

Hi I've found an Issue that I've reproduced on 3 Workflow 7.6 Servers

In the Web Form editor I add a simple button then I edit the button, in the tab Appearance I'm  going into the Style Editor via the "..." button 

And I've the Error below :

the same with the details : 

Can anyone can try to reproduce ? I've reproduced 3 times but I was using the same install package for the 3 servers.

Or if it's a bug, a fix.

The version displayed in the Help > About menu of the designer is : 7.6.4383.0

Thank you 

Geofrfoy