MATLAB: Error using writecell() : Permission denied

folder permissionsopening files

I currently have code in FolderA which runs a function that needs to access csv files in FolderB, but I am being denied permission to edit/enter the folder and its contents, though I (should) have full admin privilages on my computer.
folder = 'C:\Users\...\FolderA\...\FolderB'  % folder I want to access containing several csv files
if ~exist(folder, 'dir')
    mkdir(folder);
end
fullFileName = fullfile(folder, 'SRM_design.csv');
titles={'A', 'B', 'C', 'D','E','F','G','H','I','J'};
M={300,1,0.05,625,14.7,12.4,0,1,15,0.97};
M=[titles;M];
fname='fullFileName';
writecell(M,fullFileName);
When I run the above within my function, I get this error:
Error using writecell (line 149)
Unable to open file 'C:\Users\...\FolderA\...\FolderB\filename.csv' for writing:
Permission denied
When I run the same function within FolderB it works fine.
I will need to access this folder several times within the code and will need access to the files edited within FolderB.

Best Answer

Checked to reconfirm function runs properly within Folder B. When it didn't work I realized that the document was open in excel and therefore locked for editing. After closing the document it worked just fine again within both folders.