Well, got the same problem.
As for uploading all the files - I am sure that uploaded as needed.
The mistake was not in 68 but in 67 line, but the same function, soi i think the line doees not matter much.
I decided to delete the condition (there is condition if in the line 67)
if (!is_admin($admin)) {
echo "You don't have permission to access this file !<p><a href=\"$login_url\">Login as Admin</a>";
cpgfooter();
die();
} The installation went further.
When updating the tables of Postnuke 0.750 only one mistake occured (that may be the matter of another mistake I have seen in the Russian nuke forums at postnuke.ru): install.php tried to insert the information in the table
db_name._modules, so that is why sometimes people install the CPG and it does not appear in the administration menu (that is my quess so please do not beat me if I am wrong).
Unfortunately I cannot add the needed information in the table nuke_modules manually, 'cause cannot access the db manager from work ;-). In the evening will try to do that and inform on the results.
After updating all the tables except nuke_modules (as install.php informed me), I changed a install.php having added prefix nuke manually in the file and tried to run it again, but got the message "The install/upgrade has already been run successfuly for "coppermine" and is now locked".
I understood that most of installation is done and decided to access the module directly by link
http://myhost/modules.php?op=modload&name=coppermine&file=indexgot the message "Fatal error: Call to undefined function: is_user() in ***/modules/coppermine/include/init.inc.php on line 34"
well, i did not give up

I tried to reach the admin menu.
on the link
http://myhost/admin.php?module=coppermine&op=mainI got the message:
Fatal error :
module = coppermine
op = mainon the link
http://myhost/index.php?module=coppermine&type=adminI got the message:
Failed to load module coppermine (at function: "main")This is where I stopped, just 'cause I am confused as much as possible

.
Could anybody explain these bugs? Would greatly appreciate.
If any questions appear will give the best answers I can.
Thnx in advance.