I've always thought that the only particle which is correct to use with 会う is に：
But I've come across the sentence:
Is it correct? If it is, when shall we use と with 会う and when shall we use に?
と is a rather symmetric particle overall: 'I met Tanaka' has the sense of 'Tanaka and I met'.
に is less symmetric: e.g. I went to Tanaka's office to see him. It may also be a difference of status, rather than of motion: 社長と会いました seems pretentious because it creates an equality of sorts between the CEO and me.