Apostrophe: &#039 or '?

[gigicop]

Hi,
I'm translating some modules and I would like you to clarify a doubt that I have.
In some strings the apostrophe is written like "&#039" while in other strings the translators used the "'" character.
So far I've used "'" but I'm not sure if this is the right way to write the apostrophe. In fact, some time ago, I translated a xx_XX.php file using "'" for the apostrophe and when I uploaded it my CMSMS crashed.
In some important modules like the admin module, other translators used "'", therefore I suppose it should work fine in all modules, but I'm not sure about it.
Can you help me?
Thanks in advance.
Bye.

Gigi