TXnewsletter- don't have permission to access modx/manager/index.php on server?

Hi,

I get an error when trying to install the txnewsletters module

It’s when i get up to the bit where i have to add a new module...the only tabs i can see are General and Configuration although the instructions say there is supposed to be a Dependencies tab too. So i fill in the details for the two tabs i can see and go to save and get the following message:


I’ve tried everything i know and assume this is some system configuration issue??
I’m using modx0.9.6.2.

Any help much appreciated...thanks

J