@deepansrec
One of Richard’s previous comments on this post includes a link to the manual installation instructions. I simply followed them EXCEPT for two things:
On step 4. Delete the folder wp-content/plugins/all-in-one-event-calendar, I renamed the folder to ‘xxxall-in-one-event-calendar’. I had problems in the past deleting a folder before some process was complete and I wanted to go back, but couldn’t. Doing the rename hurt nothing and, if the process completes satisfactorily, you can delete the ‘xxx’ folder after you are satisfied that everything is working correctly.
On step 6: Copy the contents of the folder wp-content/plugins/all-in-one-event-calendar/themes-ai1ec over wp-content/themes-ai1ec and replace any files that are already there. This will update any theme files, while leaving any custom themes.. I first created a new folder with the correct name, then I opened the folder on my local system and ftp’ed the contents of that folder to the new folder I just created. This eliminated the possibility of the folder contents ending up in the wrong path.
Hope this makes sense and helps.