Hey Omer,
Thanks for reaching out.
I tested this snippet on my own testing site and did not the issue you describe, where once you paginate into future or past months the snippet no longer works.
Upgrading to Pro is not relevant to that issue at all.
However, these forums here are our “Pre-sales Questions” forums, so we unfortunately cannot field technical support questions here.
It doesn’t currently appear that you have a premium license with us. If this is wrong, and you do have a premium license with us, then apologies for my misunderstanding!
However, in that case please log into the account on this site that has your premium license, and then post this question in a premium support forum.
If you indeed do not have a premium license, then please post your question in our free support forums here → http://wordpress.org/plugins/the-events-calendar
We check those forums a bit more than once per week, so hopefully we will be able to get to your question there.
Thank you,
George