Skype sometime showing "Invalid Number" when calling landline

Hi friends I am using Skype from long time this is really good thing. But recently I am facing some issue with this Skype, that whenever I make call to some landline number the Skype shows, that the particular number is Invalid. But some time it won’t, so why this thing happens in Skype. If you guys have any information or any suggestion then please let me know. Any of the reply will be thanks and appreciated.

According to my information this thing happen whenever the network is not proper, or there might be chances that you are using some wrong number only. So not to worry about this issue just try to make call and if this thing happen over and over again then contact to service center.

According to my information I have not seen such issue while using Skype, so maybe you are doing some mistake to make use of Skype, may be you are missing something while using Skype to make call to the specific landline.