The size of the variable should not surpass 2047 bytes. If you do that, you'll break the variable system and any variable past ESET_OPTIONS gets nulled or not registered at all. Meaning, no application, bugged or buggles will be able to read those variables using Microsoft programming practices. (One could read them directly by accessing the Registry, but that's not how it's done!)
On pre-Vista systems, it also matters the size of the entire block of variables. On post-Vista, it doesn't. You can add as many as you like, as long as they follow the above rule!
1119 seems to fix the issue, I don't know for sure. People should just copy the string and measure it in a notepad/n++. Less than 2047 it's OK.