Thanks Elron1024, I checked the module settings and found the cache is already set to 0. But check what I also found out. I compared the source code ( using view source in IE) for the same page - the one that includes the datagrid module - one using DNN 4.3.2, the working one, and another using DNN 4.3.3, the one that does not work, and found that both sources are identical except for one thing:
----------------------In DNN 4.3.2, and starting on line # 10:
<div>
<input type="hidden" name="__EVENTTARGET" id="__EVENTTARGET" value="" />
<input type="hidden" name="__EVENTARGUMENT" id="__EVENTARGUMENT" value="" />
</div>
-----------------In DNN 4.3.3
<input type="hidden" name="__EVENTTARGET" id="__EVENTTARGET" value="" />
<input type="hidden" name="__EVENTARGUMENT" id="__EVENTARGUMENT" value="" />
----------------------
As you can see the only missing thing in DNN 4.3.3 is the <div></div>. but everything else in both sources matches line by line ( thanks to notepad++). Could this <div></div> cause the problem? I tried to add the <div> manually but I'm not sure what file I need to add it to.