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