Fnn

Explanation
The
system detected an error while processing a Supervisor Call (SVC)
instruction. The last 2 digits of this completion code, nn,
are the operand of the SVC instruction in hexadecimal. For example,
completion code X'F0D' means that the error occurred while
the system was processing SVC X'0D', that is, SVC 13.
One
of the following occurred: When nn is equal to 13, 14, 17, or 37, recovery
for OPEN/CLOSE/EOV failed to recognize a passed internal abend code.
Register 12 contains the passed internal abend code.  This is probably
a system error. If the ABEND is accompanied by message IEC900I, the
code was issued by DFSMSdfp and
the code explanations are provided in this section . If the
ABEND is accompanied by error messages starting with message prefix
EDG, the code was issued by DFSMSrmm. See z/OS DFSMSrmm Implementation and Customization Guide for
explanations of the codes when they are issued by DFSMSrmm.
When nn is not equal to 13, 14, 17,
or 37, the system detected an incorrect SVC instruction.

System action
Depending on the value of nn,
the system does the following: When nn is equal to 13, 14, 17, or 37, the
system records the unrecognized internal abend code in register 12.
It issues message IEC900I.
When nn is not equal to 13, 14, 17,
or 37, the system records in register 2 the address of the request
block prefix for the program that issued the incorrect SVC.

Operator response
If the system programmer asks for an SVC dump,
set the following SLIP trap:
SLIP SET,COMP=Fnn,ACTION=SVCD,END

System programmer response
Depending on the value of nn,
do one of the following: When nn is equal to 13, 14, 17, or 37, see
message IEC900I. Search the problem reporting data bases for a fix
for the problem. If no fix exists, ask the operator to set a SLIP
trap to obtain an SVC dump. Contact the IBM® Support
Center. Provide the SVC dump and, if available, the logrec data set
error record.
When nn is not equal to the above values,
do the following: For recently installed SVCs, if the number (nn)
is X'C8' thru X'FF', it is an installation defined
SVC.  If the SVC number is X'00' thru X'C7', and
you continue to have a problem after following the next steps, search
problem reporting databases for a fix for the problem. If no fix exists,
contact the IBM Support Center. Correct the error as follows: Make sure that the SVC instruction was not incorrectly modified.
Check the operand against the valid codes for the system being
used.
Determine if the SVC that was issued has been installed correctly
in the system. For a detailed description on creating installation
defined SVCs, see z/OS MVS Programming: Authorized Assembler Services Guide,
or z/OS MVS Initialization and Tuning Reference. Ensure that the EPNAME specified in IEASVCxx parmlib member or
on the SVCUPDTE macro, matches the name specified in the LINKEDIT
JCL used to link the SVC routine into SYS1.NUCLEUS or the LPA.
Ensure that the system has been reIPLed after the linkedit of
the SVC routine to the modified LPA.  See z/OS MVS Initialization and Tuning Reference for
information about the CLPA and MLPA system parameters.

Run the job step again.

Also, the are a couple of other common situations that
can cause this ABEND: Programs coded or compiled to run on CMS systems commonly issue
SVCs 200-204 (X'C8'- X'CC').  If one of these objects
is linked into an MVS™ load module,
it will get  the corresponding Fnn ABEND when that instruction is
executed.  The fix is to write  such code so that it detects which
operating system it's running on and execute the  appropriate instructions.
Another variation on this (and more likely to occur) is REXX EXECs that
have been  compiled into object format.  These have to be link-edited
with the appropriate  stub code CSECT (EAGSxxxx).  If the compiler
output is linked into a load module  by itself (or the entry point
is not set to the stub), the resultant load module will  get a FCA
ABEND.  The programmer should refer to  IBM Compiler and Library for SAA REXX/370 - User's Guide and
Reference for details.

Source
Supervisor control