I cant bind my strife key from the keyboard (e q) to my mouse (4 5) button.

Hello guys
I have a question
I already binded my default strife buttons( e q) to my mouse button (4 5), its all right, its functioning.
The problem is when i click both 2 buttons on my mouse to move forward, and at the same time i want to use strife, it doesnt happen anithing only just strifing the left side, the other button what should movr my character to the right doesnt function.
I want to note that both buttons function like excepted, when i dont move forward with my mouse and try moving with W.
If somebody can help me it would be great!