Thanks Jo-Anne for replying.
Yes I am opening the form in the browser. Just after I got your reply, I checked the design checker again and noticed it has a problem with the digital certificate which I removed, but I doubt if that's the problem because I have succesfully published it before. I guess the errror occured today while working on the form.
I have been having this problem for sometime now. I have tried;
a) Deleting the repeating table control and added a new one. This fixed it for a day, and the issue started the next day.
b) I modified the repeating tables post back settings to always. This also fixed it for a day, and it started again the next day.
c) This morning, I changed the post back setting to never. This has also fixed it for now, not sure what will happen tomorrow.
Thanks for your replies and hopefully for a solution.
Regards