You may receive this error due to incorrect placing of elements in ISA segment. This make you irritated if you are not able to figure where you are missing out in spacing in your ISA segment message in X12 message. Below is the corrcet ISA segment and you could verify your ISA segment against this. Also on msdn the description and resolution of the mentioned problem is detailed.
ISA*00* *00* *02*XXXX *01*XXXXXXXXX *091210*1153*U*00401*000000142*0*P*>~
http://msdn.microsoft.com/en-us/library/bb968029(BTS.10).aspx
Cheers,
Vishnu