Here is a article from Autodesk on the issue.
Issue
Toolbar button icons are smiley faces instead of the icons that were specified.
Solution
There are two scenarios in which this problem occurs:
The software cannot find the toolbar button icons.
There are not enough free resources to load the toolbar button icons.
These issues can occur for several reasons:
Issue
The toolbar is referencing icons in a DLL file or bitmap files for the images, and those files have been moved and/or the files are outside of the support path used by the software.
Solution
Move the files back to their original location, or add the new location to the support path.
Issue
The buttons were moved from one menu group that used a DLL file for its resources, to another menu group that does not use the same DLL.
Solution
In this case, your the software may have problems finding the icons when restarted.
To resolve the issue:
After moving/copying the icon to a toolbar in a different menu, right-click the icon and choose Edit to edit it.
In the Button Editor, choose Save As, and save the icon to a folder and file name that is accessible to you.
Open the icon saved in the last step from the new location.
Choose Save, and then choose Close.
Choose Apply and Close in the dialog boxes, and then restart the software.
Issue
A flyout button needs another toolbar to fill in the flyout.
Solution
If the software cannot find the second toolbar to fill the flyout (for example, if the toolbar is in another menu group that is not loaded), it fills the flyout button with a smiley.
To resolve the issue, load the missing menu.
Issue
The software cannot load the icons, because it cannot open any more files.
Solution
This situation can occur if the software has already opened the maximum number of files permissible. Refer to the following technical solution for a resolution to this problem:
TS43358, "Maximum number of files that can be open simultaneously."
Issue
The icons cannot be loaded, because the operating system is running low on resources.
Solution
There are several reasons why this situation can occur. For example:
Running multiple instances of your Autodesk® software
Running several programs simultaneously
Not enough free disk space
Not enough free physical memory (RAM)
To resolve this issue, you need to free up/increase system resources.
Note: For more information about toolbars and customizing toolbars, refer to Help in your Autodesk software (Customization Guide > Custom Menus).