Lrnhelper not recognizing discrete code

I took the 'Mute' code from the Remote Central Hex database for the STR-DE525 device and pasted it into the IR code box on lrnhelper, in preparation for injecting it into the 'Learn' function in Homeseer. However, apparently lrnhelper does not think this is a valid IR code, since the option to inject the code is not enabled. Lrnhelper is working - there are some codes that do enable the inject option, and when enabled I am able to successfully inject the code into Homeseer. But lrnhelper does not allow this particular code to be injected.
Does anyone know what the problem is? Here is the code:
0000 0067 0000 000D 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0430
Thanks in advance for your help.
Does anyone know what the problem is? Here is the code:
0000 0067 0000 000D 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0018 0000 0430
Thanks in advance for your help.