Error: L6218E - undefined symbol

Hi,

I am experimenting an issue with my Keil project.
I am using the STM32CubeF7 HAL to programa a module I need.

I search some info about similar problems and I found some comments about declaring a function but not defining it as the cause for all of this linker "undefined symbols" problems.
In my case I have the "stm32f7xx_hal_uart.h" and the "stm32f7xx_hal_uart.c" added to my project so I think the problem could be different.

The error throw by Keil is the same I found in other posts :

linking...
.\Objects\uart_hal_cube_st_testing.axf: Error: L6218E: Undefined symbol HAL_UART_DeInit (referred from hal_communications.o).
.\Objects\uart_hal_cube_st_testing.axf: Error: L6218E: Undefined symbol HAL_UART_Init (referred from hal_communications.o).
.\Objects\uart_hal_cube_st_testing.axf: Error: L6218E: Undefined symbol HAL_UART_Receive_DMA (referred from hal_communications.o).
.\Objects\uart_hal_cube_st_testing.axf: Error: L6218E: Undefined symbol HAL_UART_Transmit_DMA (referred from hal_communications.o).
Not enough information to list image symbols.
Finished: 1 information, 0 warning and 4 error messages.
".\Objects\uart_hal_cube_st_testing.axf" - 4 Error(s), 3 Warning(s).

But, as I said, I have those functions declared and defined inside my project.
Anyone could help with this?

Thanks in advanced,
Omar