We have been using NextGen gallery successfully for some time.
We have a 20mb limit on uploads, which has not been a problem.
Today, I uploaded 13 meg of photos in 2 batches to a new gallery and got, for each photo...
(Error : Exceed Memory limit. Require : 33.81 MByte)
..as an error message for each photo's thumbnail creation. The photos themselves are fine -- they display in the admin preview. But I cannot create thumbnails.
Again, we have not had this problem until today and have made no changes to our server config.