IDE New Project needs writable memory

In addition to what wombat states:

Have you specified an explicit pin of avalon type "write" or "write_n" to the external SRAM? This would tell the wizard that your memory is writable (basically achieving what wombat suggests with a manual edit of the file).

My concern is that you get your control sigaling correct so that the RAM can be physically written to in hardware. If the SRAM chip you're using has a *common* pin (rather than separate read and write inputs), write/read_n for example, I'd reccomend that you specify the 'write' pin and leave read_n out; Avalon should infer reads automatically if your master asks for an address and does not assert write.