Yeah it's this, according the bottom of the image you put it in caps "PROP_STATIC"That happens to me when I write "prop_Static" (with a capital S) - I guess the entity tool is case-sensitive. Set it to another entity then change it back to prop_static, and make sure it's all in lowercase.
Otherwise, it's possible you just spelt it wrong.
It's actually a picture of someone who worked at Valve back in the day.