Hi Princess,
If you want 256 KB (assuming kilo-byte) of ram, that is 256 * 1024 = 262144 bytes
To store that many bytes, assuming that your memory is byte-addressable (location 1234 referts to 8 bits, location 1235 refers to the next 8 bits), you need to find the next greatest (or equal) power of 2. So:
2^0 = 1
2^1 = 2
2^2 = 4
2^3 = 8
...
2^18 = 262144
So, ADDRESS_WIDTH is 18, not 131072. The ADDRESS_WIDTH parameter refers to how many wires represent your address (or, how many bits).
What's probably happening is that your synthesis/simulator tool can't handle a bus width of 131072 for a vector - this is incredibly large.
The other warnings are probably due to the same issue, as your synthesis/simulator tool appears to have assumed that the width of RAM is 0.