It probably does not have anything to do with the extensions themself.
Looks more like a random bug of Extension Manager UI.
On Mon, Mar 6, 2017 at 5:59 PM, Keith Davis <laurinkeithdavis(a)gmail.com> wrote:
  Well, maybe I’m crazy, now it's only happening for
the Let’s Encrypt
 extension.
 On Mon, Mar 6, 2017 at 10:57 AM, Keith Davis <laurinkeithdavis(a)gmail.com>
 wrote:
  I installed the Let's Encrypt extension and
got this message:
 Failed to execute the [velocity] macro. Cause: [Illegal char <:> at index
 4: wiki:]. Click on this message for details.
 So I created this issue:
 
http://jira.xwiki.org/browse/LENCRYPT-3
 But then I realized, that I get this same error for one other
 extension: Icon Theme Application
 Any ideas?
 --
 Keith Davis
 214-906-5183 <(214)%20906-5183>
 
 --
 Keith Davis
 214-906-5183