You attempted to set a data breakpoint whose Address is misaligned with respect to its Length. 

If the data breakpoint has a two-byte length, then the Address should be aligned on a two-byte boundary. Similarly, the Address of a four-byte data breakpoint should be aligned on a four-byte boundary. 

You can still set this data breakpoint, but if you do, the breakpoint will be set on an address that is on an appropriate boundary. This can trigger the breakpoint in unintended situations.