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I have had the same problem with you. If you go to the cache/ folder, you will see the file adminmenu.php contains nothing (the size is 0).
You can temporarily resolve it by overwrite the adminmenu.php with the one which generated by a cloned site of your site. Then chmod the cache/ to 705 in order to prevent apache overwrite it. Otherwise, whenever you make change in the admin, apache will write back the 0 size file and your admin menu will gone away.
This approach is not recommended because you should update manually the files in cache/ and templates_c (of course this folder will suffer from same prob).
As my point of view, the problem come from the setting of the server which prevent apache to write to files. For this situation, you cannot do the upload
.
You can refer to my problem
here!I am looking for a good idea about this.