Twitter get n-number of timeline from each user (loop)

Hi Oole,
Thank you very much for the reply.
I always get this error:
Execute failed: 401:Authentication credentials (https://dev.twitter.com/pages/auth) were missing or incorrect. Ensure that you have set valid consumer key/secret, access token/secret, and the system clock is in sync.
{“request”:"/1.1/statuses/user_timeline.json",“error”:“Not authorized.”}

This only happens when I loop through them…
It does not always second, but after some loop, it can happen.

Is it about the limit?

+Edit
I added partition before taking column to variables. So I took 4 random users, getting 5 tweets for each user.
Sometimes it works, sometimes it return the above error.

Any idea why this happens?

Thanks!