The culprint is a known conflict with emoticons shortcuts. A simple search on the forum for "
[Messenger Plus! Sound] - Data{" will show many threads which give you the solution.
So make sure you don't have any shortcuts to custom emoticons which might conflict with the special string which is used by Messenger Plus! to send sounds.
For example, if you have a custom emoticon with the shortcuts "!" or "{" or "}" or "[" or "]" or "*" or any other character or character combination which is in the special sound string which is used by Messenger Plus!, it will conflict with it.
So, change the shorcut to all those specific emoticons and it will work again.
Also make sure you have downloaded the latest version from the official website:
http://www.msgpluslive.com/. This interfearance should have been fixed in the latest version.
And make sure you did not tamper with Messenger itself or that you are running some patch which might change some localization resources in Messenger.
It is a bad idea to use emoticons for normal alphabetical letters anyways. It quite often is also very annoying to your contacts.
EDIT: like robert_dll already hinted at.... (I should've read better)...
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