hye i have a problem with drop down menu on notification and settings image button.i cannot click to expand the dropdown menu.

like this:

i do inspect on browser but got this error:

but i already check my file and code that i have include it but somehow it cannot be found.

also i have check my file location:

i dont know what is the problem.Is there anything else that i not include into my project?please someone help me.I have already try other solution that provide by others but it still cannot function at all.

Here my full code for that page: