If you try and import a web URL in AX 2012 R2 CU6, you will get this error. Try it on any standard URLs and the bug is still there.
For a work around put a backslash in front of the URL and it should work now.
You could make a code fix but I think its best Microsoft fixes it.
If you want to make the fix yourself then have a look at this method \Classes\sysEPWebPageDefinition\getPageUrl.
It looks like it was introduced in CU6. You can even see the Microsoft bug number and what they tried to fix. They were trying to cater for leading backslash but ended up breaking it.
I have logged it with Microsoft. I will update once I receive a response.
Update 2013-10-03 - Hotfix was provided from Microsoft.
For a work around put a backslash in front of the URL and it should work now.
You could make a code fix but I think its best Microsoft fixes it.
If you want to make the fix yourself then have a look at this method \Classes\sysEPWebPageDefinition\getPageUrl.
It looks like it was introduced in CU6. You can even see the Microsoft bug number and what they tried to fix. They were trying to cater for leading backslash but ended up breaking it.
I have logged it with Microsoft. I will update once I receive a response.
Update 2013-10-03 - Hotfix was provided from Microsoft.
KB Article Number (s) : 2894068