I thought it was general liability insurance at first but I am now almost convinced that E&O is what they are talking about.

The wording is...

"...to protect the public against a violation of Subchapter G."

Subchapter G from the Texas Occupations Code regarding inspectors is short and sweet and says...

"SUBCHAPTER G. PROHIBITED ACTS
Sec. 1102.301. NEGLIGENCE OR INCOMPETENCE.
An inspector may not perform a real estate
inspection in a negligent or incompetent manner."

"Negligent and incompetent" is the term TREC uses when an inspector has not followed the SoP. In other words, when the inspector has missed something. Now that's starting to sound more and more like errors and omission insurance to me.