The 5 custom emoticons limit has nothing to do with Plus! customsounds, its a MSNM thing.
I suggest a reinstall of MSNM. If a regular reinstall doesn't work you can try a totally clean install. To do that uninstall MSNM, reboot, remove all folders pointing to MSNM in Program files folder and the MSNM one in C:\Documents and Settings\<username>\Application Data\Microsoft (removing this folder will make you loose all customemotes and backgrounds you have - and those of all who ever used your MSNM, if you only want yours to be gone find out wich number corresponds with your account
here and remove that folder. If you don't see this folder it means you have folders hidden, to make em visible go into a folder and in the menu choose "tools" go to "folderoptions", then to view tab/second tab. In the list you see there scroll to hidden folders/files and check the box to show them), reinstall MSNM.
If you want to get rid of the 5 custom emotes limit you can install
SPNG, this has the option to remove this limit.
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