Works/doesn't work. Unknown cause

Hello,

I'm doing a project with arduino and, although it works just as I want, sometimes it seems to fail.
I'm using a GSM shield to send sms and make calls in certain cases.
The project is an alarm system that, right now, only have two options: electricity off or low temperature. Everything runs accordingly, but sometimes something fails, making the reading really slow (or so it seems), which turns into not sending the messages. I have to reset several times until I see it working again, in which resets send the previous message requested.
For what I've seen, after sending all the messages, it usually starts working fine again.

Can you give me some suggestions to test? I was wondering if it could be about memory of the pointers, as I'm using them, though I'm not allocating any memory at all, neither cleaning (not sure how to do this in arduino). Maybe it could have something to do with too much processing in the GSM Shield. But I don't really know how to deal with this.

Any help will be grateful.

Best regards,
Rhen

Where is your code?

I doubt this will be enough to understand it.

Quite right. Now, go read the stickies at the top of the forum. I'm sure something will occur to you before you get done.