Look at your reject message (which I've added field separators into for readability):
8=FIX.4.4|9=125|35=3|34=4|49=10063|50=testsubid|52=20140210-16:05:44.231|56=ICE|45=4|58=Incorrect data format for value|371=828|372=AE|373=6|10=101
See fields 371 and 372. Those fields tell you that field 828 is wrong in an AE message. Field 45 tells you that the rejected AE message has seq number=4.
From there you should be able to figure out the bad field that is being sent to you.
As to your ICE-specific issue:
Check ICE's latest spec (2.0.34 at time of this answer). "S" is indeed a valid value. You'll need to update your DD with all valid values, or perhaps just change the field to a string (or char) and get rid of the enumeration list altogether. If you delete the enumeration list, QF/n will accept any value of the correct type (e.g. string or char).