Error (XST): translate terminal to FCT

I am using version ISE7.1 and I have just come accross the same erro message.

here is the text vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv Optimizing FSM on signal with gray encoding.

------------------- State | Encoding

------------------- 00 | 00 01 | 01 10 | 11

------------------- failed to translate terminal to FCT

$n0035[18] = If $n0017 Then $n0061[18] If $n0018 Then $n0063[18] If $n0019 Then $n0065[18] If $n0020 Then $n0067[18] If $n0021 Then $n0069[18] If $n0022 Then $n0071[18] If $n0023 Then $n0073[18] If $n0024 Then $n0075[18] If $n0025 Then $n0077[18] If $n0026 Then $n0079[18] If $n0027 Then $n0081[18] If $n0028 Then $n0083[18] If $n0029 Then $n0085[18] If $n0030 Then $n0087[18] If $n0031 Then $n0089[18] If $n0032 Then $n0091[18] If $n0033 Then $n0093[18] Default 0

--> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ So it seems very similar and I could not find neither the explanatio or solution up to now.

Hope someone can help!

Erwan