eshell alias not working properly

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Hi

I seem to be having problems with my eshell aliases,
e.g. the following alias in the aliases file doesn't work in eshell 2.4.2, 
emacs 24.4.1 
============ 
alias ff 'find-file $1' 
============ 
error message as is is given below 
> find-file $1: command not found 

Any ideas what may be going wrong?
Thanks in advance.