Spot the error: He suffered (a) / from fever when he was interviewed (b) / for the job. (c) / No error (d)

The error is in part (b). The sentence describes a temporary condition during a past event, so the past continuous 'was suffering' would be appropriate, or the noun 'fever' should be preceded by an article ('from a fever'). The standard usage is 'suffering from a fever' or 'suffered from fever' is often considered incorrect without an article in many style guides. Hence (b) is the part containing the error.