Copying files in UNIX

I have Folder1 with 12000 files in that folder.
I can easely copy all files from this folder to another folder using commands:

su
Password: xxxx
cp ./Folder1/* ./Folder2/

I created a script in csh – “copyFiles”,
again :
su
Password: xxxx

then I use “exec” command to run script in the same shell:
exec copyFiles
it copies portion of Folder1 and gives me an error
“Argument too long”
What I’m doing wrong?

Thanks