=IF(OR(ISTEXT(L26),ISTEXT(L29)),"Error in C12 or C15",(L26+L29))

When I started working this past Dec the formulas were already put in by someone else. Somewhere along the way I started having to auto fill and calculate the hours I worked. I would like to fix this so when the next person comes on board and I have to share the time sheet that it is correct for them. I do believe this particular box is the only one with an error. It is Sunday thru Saturday but this particular err or is only on Friday's after lunch time to check back in for the rest of the day. (If that matters)