Did you edit your class2.php in v0.7.3? the 0.7.3 replaces some files that are needed to edit to work. You may have to check it again. Notably class2.php, comment.php, mailout.php and others which may use the ob_end_flush ()
for those who still get blank page, you have to uncomment the ob_start(); line at class2.php.
somehow you need to uncomment it first and comment it back when u use coppermine gallery
you have to do it step by step and not paste everything and install.
Ignore my file posted before this >.<
-Install v0.7.2 (provided you fix your class2.php and installer_handling_class.php)
-Copy Paste patch 0.7.4
-Fix 0.7.4 files