when i included the LiquidCyristal library in the my_menu.h library it didn't work
"it didn't work" has to be the most overused phrase on this forum. It doesn't tell us anything.
"When I use this code, it fails to compile, with this error message" tells us something.
"When I use this code, it compiles, but nothing appears on the LCD when I run the code" tells us something.
"it didn't work" tells us nothing.
i also get the same error if i don't include thwe library, nowhere.
Lucky you.
If you care to quit dancing around, and post some code and error messages, we'll be happy to help.