V-Ray and Corona toolbar buttons missing icons in 3ds Max

Issue:

After launching 3ds Max some or all of the V-Ray and Corona toolbar icons are missing. The toolbar is still functional, but the icons do not display.

Causes:

V-Ray and Corona toolbar corruption.

Solution:

To solve issues with missing VRay or Corona toolbars in 3ds Max:

• Update 3ds Max to the latest version.
• Perform a Clean Uninstall of V-Ray for 3ds Max.
• Perform a Clean Uninstall of Corona for 3ds Max.
• If the issue persists, do the following:

1. Run a Repair on 3ds Max.
2. Contact Chaos Group support or Corona Support for additional troubleshooting of the plugin.

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Source: https://knowledge.autodesk.com/support/3ds-max/troubleshooting/caas/sfdcarticles/sfdcarticles/3ds-Max-V-Ray-Toolbar-buttons-missing-icons.html