Field data not saving/storing to database

Hi,
I've been having an issue for quite some time now where when data is entered into fields, it just isn't saved. I had it happening on a website I'm trying to set up, I'm still having no luck with it and each time I try and enter data, a lengthy error message appears. I've tried lots of things, but it's become too much for my small php knowledge.
So, I was ready to almost start from scratch with the other site, but I've been working on a completely different website and I've noticed that the same thing is happening.
This time, there's no lengthy error message, but whenever I try and input data into cck fields and save it, it just won't save. I was tearing my hair out trying to figure out why the fields wouldn't display anything until I realised that they won't actually save any data.
I've been using Drupal for a long time now and I've never had this issue before, I can't understand why it's happening at all. Both websites it's happening on user profiles using the Content Profile module.
It's also not just my computer, I've tried using other computers and other browsers and still the same issue.
I was ready to accept the issue on one site, and put it down to just a mis-match of modules or something like that, but now that it's happened again on a second site, I can't simply let it be. This is a pretty major setback, and I have no idea why it's happening nor how to fix it.
Can anyone shed some light on the issue and perhaps help me out?