The Malleable Linkset main script has exceeded the viewer editor's default memory size (64K characters). This means that attempting to add or paste characters in the script window results only in a sound being played.
However, it's an easy hack to increase that limit. Look for the XUI directory in the viewer install directory, and the language you're using. For example, the default for someone using Firestorm's English language version under Windows is "C:\Program Files (x86)\Firestorm-Release\skins\default\xui\en". In that folder, edit the XML file "panel_script_ed.xml" and within "text_editor", change "max_length" to the desired value. At the time of writing, this is "500000" on my install, but it can be much more if necessary.
You'll need to restart your viewer, of course.
Source: this page