@Somasekhar I think the error message is a little confusing. From the software standpoint, the error is unknown – it is merely suggesting the built-in shell screencast as a possible reason (probably because it is a common mistake that users make), but that is not the problem in your case. The problem is with MP4, most likely due to a need for unsupported licensed codecs. Please click on the arrow to the right of “Record as MP4” and select either GIF or WebM. I have tested here, and I see the same error message as you with MP4, but both GIF and WebM are working fine for me.