From AXI spec:
SLVERR, slave error
The SLVERR response indicates an unsuccessful transaction.
To simplify system monitoring and debugging, this specification recommends that error responses are used only for
error conditions and not for signaling normal, expected events. Examples of slave error conditions are:
• FIFO or buffer overrun or underrun condition
• unsupported transfer size attempted
• write access attempted to read-only location
• timeout condition in the slave
• access attempted to a disabled or powered-down function.