It looks like you never assign C{k} unless there is an error. Maybe you should assign C{k} after the end statement that end the try catch block.
In general I think a try catch is best for when you get unanticipated errors. If it is a condition you can test for, like a zero in a denominator, too many iterations etc it is better to just check for that condition using an if statement and handle it more precisely.
Also it looks like you don't need to use a cell array to collect your results. You could just preallocate an array
C = zeros(N,7)
before your loop and then just directly assign
C(k,:) = [x f1.parameter1 f1.parameter2 f1.parameter3 f1.parameter4 f1.parameter5 parameter6]
If you wanted to find out what rows didn't get assigned just look for rows that are all zero. You could also do this maybe even cleaner by preallocating an array of nan of not a numbers and then checking for which rows still have NaN values, for example using isnan
