I would say, "No, absolutely not."  Think about the effect that would have... it would create a right for the client to file a claim for a lost THEY caused, not just the ones caused by YOU. An E&O policy generally states:

"We shall pay on your behalf those amounts... you are legally obligated to pay as damages resulting from a claim..."

"You" means the insured.  When you add a third party as an insured, you are basically expanding the coverage to include any potential claims they cause.  Think of it in terms of an auto policy.  If you add your son to your auto policy as an insured, you are basically telling the insurance company that you want them to cover him for his accidents, as well as your own.  And, what happens?  They evaluate the additional risk and raise your premiums.

Sticking with the auto-policy theme, I think what your client would really be asking for is to be added to the policy as a loss-payee.  This is what they do with your bank when you have a car loan.  If the car is totalled, they pay the bank instead of you (up to the value of their interest in the car).  However, this is unnecessary in an E&O policy since it states that they will "pay on your behalf those amounts you are legally obligated to pay." 

I don't think your client understands how insurance works.  This is YOUR policy, not theirs.  If they think you are liable for a claim, they will notify you.  You, in turn, should notify your insurer to preserve your claim in the event you are held liable.  You insurer may decide to pay the claim, or defend you - since they only have to pay the claim if you are found legally obligated to pay the client damages. 

Thus, I would never add anyone else to my policy as an insured... unless, of course, they were willing to pay the premiums.

Best,
Robert A. Franco
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