FCO390A ERROR DURING STOW stowtype FOR membername. RC=rc REAS=reason
An error has occurred during a stowtype STOW operation for member membername. The return code from STOW is rc. The reason code is reported as reason. For information about STOW error codes, see the appropriate IBM documentation.
Means basically the following:
The STOW ADD rc=4 indicates that the member being added was already present in the directory. The COPY statement does specify REPLACE, but FastCopy issued STOW ADD, rather than STOW REPLACE. It checks for the presence of the member in the output and issues STOW REPLACE if it is present.
It is possible that some other job added that member to the library between the time FastCopy checked for presence and issued STOW ADD.