We already heard of this Power Rangers Super Megaforce cameo univite letter, which caused quite some problems to those past Rangers who are interested to return. Below is an excerpt of the said uninvite letter... and it sounds really generic like the invitation letter.
To read the full e-mail, you can check this RangerCrew thread for more details.
Therefore it is with tremendous heartbreak that we have to tell you that due to the immense number of positive response to our inquiry to you all, we are not able to bring all of you to New Zealand to join us for the anniversary. Please understand that this is strictly a budgetary restraint, as we truly wish we were able to accommodate all of you in this celebration.
To read the full e-mail, you can check this RangerCrew thread for more details.