Getting 404 Error after installing OpenWrt openwrt-wrt150n-2.4 on WNR3300

I’m providing hopefully helpful information. The age and chips in your router suggest that approaches that are generally not relevant apply. 30-30-30 is not relevant to any current or recent routers. It would be a disservice to others to mention it without being clear of the context.

The 30-30-30 suggestion comes from my recollections of flashing WRT54g units, with similar hardware and OpenWrt versions, and recalling that the flash “didn’t take” on occasion. Early versions of OpenWrt used the NVRAM, as I recall, and that may be relevant to your problem.