I had this error which appeared just the same as steelerfan27 today and I resolved it with a reboot.
>>App Name
>>There is a problem completing your
>>request, Try again later.
>>
>>Error code: c101b000
>>
>>***retry*** ***close***
>>
>>when I hit retry, it downloads 50% and reverts back to the same loop.... when I hit close, it
>>closes the window......
It repeated several times so I powered off my phone and when I powered it on again the app installed fine.
I have a Nokia Lumia 920.
Paul
I had this issue last week. The error code 'c101b000' refers to a market store fault, I have checked the site (http://support.xbox.com/en-US/xbox-live-status)
and it shows it as working. Maybe if your screen lock / times out you cant continue download. n Windows phone > Settings > Wifi (scroll down to 'Advance') Click on enable wifi / connection during screen lock / time out and that should help.