You seem to have confusion between variable names and functions; the Matlab GLM function is fitlm the returned LM object is the LH variable mdl. Similar confusion is seen between table and the LH variable tbl.
Presuming the part1cdata .mat file contains an array, it would be much easier to use
tbl = array2table(part1c, ...
'VariableNames', ...
{'ATP','ABD','AIRTEMPCOLD','MOTOAIRTEMP','PRESSDISCH','TEMPDISCH'});
to create the table.
BUT, the problem seems to be some problem that isn't consistent with the error; if the .mat file were not there, then would get an error with load like
>> load part1cdata
Error using load
Unable to read file 'part1cdata'. No such file or directory.
>>
but if there's an error referring to part1cdata, then there's no other code in the pasted snippet that refers to that variable name.
We need the precise code and error message in context; attaching the .mat file would also help if there's still confusion on "who's who in the zoo"...
