Error in Concatenate. I just can't see it!.

This is very frustrating, but I'm forced to post this question.

I've been working long hours today on and old 4.6C system.

I need to make a simple concatenation but I just can't see what the error is.

I have this table:

You can see that the last two fields are of type char. Table is active and with data. Data types are also active.

And when I try to do this concatenation:

I got this error:

LW_PARAM is of type ZTPZ4M.

LT_PARAM is of type table of ZTPZ4M.

PL_LINE is type c of 100.