As DerbyDad03 says, I am pretty sure that the problem is that the button loses track of where the macro is stored.
I suggest that you save your macro in an Add-In.
You can make the Add-In automatically create the button on the toolbar complete with its link to the macro in the Add-In. Then the Add-In can be loaded on to other PC's and the button will also be loaded - although getting a custom image to load is not simple.
There are some differences in the way PowerPoint accesses Add-Ins compared to Excel or Word, and you have to save the macro in a ppt file before saving it as an Add-In ppa file.
Also, as far as I can tell, you can't edit the macro directly from the ppa file, you have to edit the code inside the original ppt file and re-save it as the Add-In ppa file.
(You can view the Add-In code if you follow the instructions to add / change the value of a registry key - see these instructions. Note that PowerPoint must be closed when you add / change the value of this key).
There are several sites that describe how to create an Add-In for PowerPoint. Here is one of them