mailing list-Newsletter issue

is there a limit to a csv file

[contentmaster]

I am using a free script for sending regular newsletters to about 7000 subscribers....however as the number of subscribers are increasing the script seems to be creating some problems -----

once I click on 'send', a few minutes later the 'error on page' and the page cannot be displayed appears!

My question is
1) is there a limit to the csv file that contains my list of subscribers (email ids) and is that the reason why the newsletter is not going to all the subscribers?
2)Or is this an issue with the script?
3) Is there a way through which i can know how many ids are no longer valid on my subscriber list?

Thanks