Could not select classical qRFC version for destination XXX

Hi Gurus

We are on ECC 6 and sending data to SRM 5 . Have created RFC users in SM59 and the RFC connection to SRM under the tab Special options , the Select qRFC Version is 1 bgRFC so we want to change it to 0 Classic qRFC , while trying to change we are getting the error " *Could not select classical qRFC version for destination XXX "*

How can we resolve this ? there is nothing on SMQ1 and SMQ2

Will award points for any response

Regards

Warona