"Succeed in" or "succeed at"
Solution 1:
Both Cambridge and Oxford's dictionaries show succeed being followed by the prepostion "in". On Cambridge English tests (FCE, CAE and CPE) the combination "to succeed at" is considered an error.
Solution 2:
I have always used 'succeeding' in followed by a gerund.
He succeeded in duping his clients for many years.
I wouldn't use 'at' in this context ever.
Further to that I agree with the post above and the suggested connotations of 'in' concerning doing well within a context and 'at' concerning doing well at conquering a task.