How not to do error messages

I am currently proof-reading a software which I haven't written (which is very funny as I am not native english speaker, but my english is better than the one of the guys which wrote this software).

And my question is: why the hell did they add an exclamation mark in each error message?

For a user, is extremely disgusting to get something like:

You are not allowed to access this resource !
It's unpleasant, rude, ugly and finally it's confusing, talks in term of programmers (that "resource"jargon which only the programmer knows to what refers with that term; even I had a hard time to discover what he meant with that)

It would have been better something more relaxed, less scaring. Something like:

An error has occurred. As you have not been active for a time, you need to enter again your login and password in order to continue, as only registered users are allowed to access this page.

I know it's longer, and it is not the best replacement one could find, but I have been reviewing more than 2000 strings of text today and I would like to find something more human in this piece of cr... err... software!