error 499 in mplab while interfacing lcd
When a C program is compiled by the High-Tech compiler (and many others) each individual source code file with .c a extension is compiled into a relocatable object file with a .obj file extension. Then a program called the linker combines all the object files together into an executable which in this case will be an Intel HEX file with a .hex file extension.

That error indicates that the linker hasn't been able to find the corresponding code for the LCD_write function so you should include the C source code file that contains the body of the function in your project.

Sometimes libraries are also distributed as .lib files that are relocatable object library files. They are essentially a collection of one of more compiled object files and are sometimes used if the vendor doesn't want to supply source code for the library. In that case you should add the directory containing the library to the linker library search path under the project settings.