Firstly, congratulations on your promotion to full membership!
I'm fairly sure that loss of posting rights in the welcome area is meant to happen. Although it sometimes occurs as a result of a random error, the "Access Denied" mesage is a fairly clear sign that your account permissions have been amended. By my recollection, this may have been mentioned before. I just had a look at the Welcome discussion section and at my end there's a "new topic" button above the list of threads there. Perhaps that is a function of my senior membership, I never knew.
Having given this a further moment's thought it seems to me that this is a feature to ensure that newly promoted members get to notice the fact rather than simply plodding away unawares posting in the Welcome area for evermore.
Now you'll have to work out which section of the forum to post your thread in instead!
“There is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
― Jacques Bergier, quoting Fulcanelli