1)
When you execute Backup Table As SQL Dump' it seems that you are 'allen'@localhost' user.
However when you execute 'select user, host from mysql.user' it seems that you are 'timemapu_shemp'@'localhost' user and when managing privileges.
Can you explain why two users are involved?
2)
“It gets about halfway through the dump, according to the progress bar, then stops.”
Is anything written to the file at all except for initial SET statements? Just open it in an editor and see what it reads like.
3)
If it worked before with same user(s) then something has changed server-side.
One possibility is that some mistake happened during a server upgrade or that the `mysql` database on the server has simply corrupted.
Is this server a server managed by somebody in your your organisation or is it a hosted server? I am afraid you will need to ask the appropriate server admin to look into this. Only a person with full admin privilege can sort it out. What you experience with SQLyog would happen with any client. Problem is server-side, not client-side.