-- abend b37
Transfer from ASCII platforms (like Unix/Windows) to Mainframe monitor ends with a B37 Abend

Main known issue is due to file format (FRECFM=F) used by the sender (ASCII side) when (true) LRECL of the file is not FIXE (the LRECL vary, so the file is physically variable records length)
On ASCII platforms, nature of files are usually variable. If the actual length for some records is lower than the declared FLRECL value used for the file transfer, the mainframe will use the FLRECL and the FSPACE (calculated on the ASCII platform) to allocate the Fixed Format file that will be probably too small regarding the effective records number to be received.
A workaround can be to force a larger file size on the mainframe using FSPACE in the CFTRECV command.
But when files to be sent are not "true" fixe type, variable record format should be used instead to avoid any issue regarding space allocated on the receiver side.