The existing screen comes up without any problem... It is in Production and I made some modification (major) to it and facing this issue in Test. Trying to resolve before I move it to Prod.
I found the below explanation myself,
MFS cannot fetch the control blocks required to process an output message or to process the /FORMAT request. The block name in the message specifies the name of the block that could not be fetched and is either the MOD or the DOF name. If it is the DOF name, the first two bytes of the name are the device type and features printed in hexadecimal. For an interpretation of these two bytes,
The MOD and DOF fetched were incompatible (not compiled at the same time). This might be caused by the use of z/OS utilities to alter the active format data set library.
This gives me an impression that this problem is nothing to do with MFS... but its with Z/OS utility!