Corporate Law Do I need Liability Insurance or E & O Insurance or both?

[Karmababy]

I want to start billing as an independent contractor for a speech/occupational/physical/music therapy business. I will be billing the patient's insurance companies and Medicaid for the various therapies. I will be paid a percentage of the amounts I bill. The bulk of the work will be done from my own home computer. The client wants me to purchase liability insurance. Why would I need this? Would E & O insurance suffice? Or would I need both? I do not expect to make more then $500 or so the first year.