concatenate field vbak-netwr

Hi Friends,

I have a small problem.

in the code below I got a short dump, says.

During concatenate the Operand <FS> is of Format "P" and it is not allowed, only strings.

do.

assign component sy-index of structure I_VBAK to <fs>.

if sy-subrc <> 0.

exit.

endif.

if sy-index = 1.

xout = <fs>.

else.

-> concatenate xout <fs> into xout separated by ','.

endif.

enddo.

How can I check and change the Data type of <fs> in this moment.

I have tried a cast like "field-symbols: <fs> type c" but I get only strange characters for this field vbak-netwr.

Can anyone help me?

Thank's Jimbob