How to export data from a graph to excel

Hi, to export data from a graph to excel the following requirement in my matlab programme has been introduced:

save_ubanks_CT.prn MTC -ascii

being ubanks_CT.prn the name of the folder and MTC the name of the variable

it turned out well in a first attempt but command window throws the following result:

Error using save

Unable to write file ubanks_CT.prn: permission denied.

Error in ej_file1 (line 209)

save ubanks_CT.prn MTC -ascii

any suggestions?