Oh, I do my fair share of babysitting (altho several clients in the last week have received my wrath this year for last-minute **bleep**; I'm getting too old for it)

But the OP implied the accountant should be responsible because the client couldn't be responsible reading his/her own mail from the IRS.  Nope, not buying it.

The previous accountant made mistakes: 

1. Changed from disregarded entity to c corp ( claiming that the LLCs officer had no ssn). Changed from c corp to s Corp ( After getting ssn)

2. Failure to notify a client about reasonable salary for himself ( filing w2)