Follow Me with Certain Extension Numbers Causes Busy Signal and Error

When an extension has Follow Me disabled, there is no problem calling that extension from another extension. However, when Follow Me is enabled, we get a busy signal and the logs show this:

[2018-07-06 15:31:14] WARNING[6562][C-00000003] pbx.c: Channel ‘SIP/1-00000003’ sent to invalid extension but no invalid handler: context,exten,priority=followme-check,2,1

The cause appears to be the extension number. We tested on two servers using extension # 1, # 2 , and # 40. This happens only with 1 and 2, but not with 40. 

I’ll log this in the issue tracker.