When you receive message XCOMM0243E INVALID OR INCOMPLETE DCB CHARACTERISTICS then check the DCB-Characteristics of the file which is to be sent by XCOM.
For example, if a file has these characteristics,
Dsorg Recfm Lrecl Blksz
--------------------------
PS VB 0 27998
XCOM cannot transfer it because these are no parameters which are supported by IBM as "LRECL=0 is valid only for RECFM=U" is stated in the IBM Manual "z/OS V1R12.0 MVS JCL Reference (SA22-7597-14)". Certainly there might be tools or programs which are able to allocate such files.
But bottom line is that XCOM supports all files which are allocated using ISPF-Option 3.2 or any JOB following the guidelines of the JCL Reference.