Transfer Valves closed
What exact ECAM message is being seen? How much fuel was in the inners at the time? Which flight phase did it occur??? All these have a bearing to indicate if there is a hard or spurious fault!
The system is such that (in general) the forward L & R XFR valve are controlled by one set of low level circuits (in both L & R wing) and the aft set of L & R XFR valves controlled by another set of low level sensors (in left and right wing).
What does this mean in practice?? In short if you get to such that the low level sensors in the L or R inner tank (approx 750 kg) go dry then the related XFR valves for those sensors (either fwd or aft) on both wings opens.
The ECAM warning L(R) OUTER TK UNUSABLE should only occur at the point that the XFR valves are commanded open (due to the BITE logic). Also a failure in the control circuit (relay or otherwise) would only fail the forward or aft XFR valves. There will need to be a dual failure to fail the forward and rear on the left and right wings such that the ECAM indication L OUTER TK UNUSABLE and R OUTER TK UNUSABLE appear at the same time!!!
Airbus have released a TFU which covers XFR valve warnings that happen on both L & R wings at the same time - worth checking it out.
In short one of the recommendations for L & R XFR valve messages is to reset the FQIC (C/B's 1QT and 2QT). What this does is perform a Power on Bite of the fuel sstem which cycles the XFR valves, and clears the problem.
Hope this can give some guidance.......