How to solve multiple definition of `__vector_11' error

I want to use 3 libraries enable interrupt, servo and SoftwareSerial/AltSoftSerial

when I use the enable interrupt, servo and AltSoftSerial I get "multiple definition of `__vector_11' " error

and when I use enable interrupt, servo and SoftwareSerial I get "multiple definition of `__vector_3' '' error

How to solve this problem.

did you try using ServoTimer2 library instead?

Using ServoTimer2 is probably the best option.

There is also NeoSWSerial.

The best way to solve this is perhaps using a board with a spare hardware serial port. For example the Arduino Leonardo or (Pro) Micro. Or one of the new processors, Arduino Due, Zero, or a Teensy board.

It is also possible to add a PWM module to create Servo signals with a hardware chip.