When something doesn't work, you should report back showing what you tried so that people can troubleshoot for you. In the above, you have not used the parens correctly, and have added the one in the wrong place. Use:
{hrpersnl.p_lname}&" "&{hrpersnl.p_fname}&" "& left({hrpersnl.p_mi},1)
If the middle name can be null, use:
{hrpersnl.p_lname}&" "&{hrpersnl.p_fname}&
(
if isnull({hrpersnl.p_mi}) then "" else
" "+ left(({hrpersnl.p_mi},1)
)
-LB