Problems using Calendar and Diary mode in Emacs 23.0.60.1

[Richard Fieldsend]

Hi,
I've been using Emacs for all my text editing needs for a fair few years. I've 
also used the calendar and diary (I especially like to generate the month 
calendar with the appointments in place as a LaTeX file).

However, I haven't used it in a while for various reasons, and in the meantime 
I've done two things. 

i) I upgraded to a new version of Emacs

ii) I 'rationalised' my .emacs files splitting it into various files which 
provide things like markup, time and date functionality etc. 

In normal usage these changes have appeared to cause no ill effects, until I 
tried to add a new diary entry to my calendar and diary.  Starting the calendar 
in the normal way (M-x calendar) and selecting a date before hitting 'i d' for 
insert day, I get the following error message (taken from the *Messages* 
buffer):

Symbol's function definition is void: diary-insert-entry

Is this likely to be caused by my rationalisation, or something else. I'd like 
to get this working again if possible (rather than resorting to my filofax!)

Thanks in anticipation

Richard