The upload resampling is using up all your PHP memory.

Your options:

1. don't allow such imgae file uploads
2. increase your php memory
3. turn off resampling (security implications here)

The image file you are uploading is too big for PHP to process with your current memory limits. Exploding an image into raw data then processing it massively increases its size. Basically your 2 MB file turns into 30 MBs of memory when this happens. Specifically the memory issue is happening from imagefill PHP function.

Also note this isn't specifically a file size issues. It's pixel data that's the problem. The higher the dimensions of the image the more pixel data it needs to store in memory to process the image. So if you've like a 2000x2000 that's a ton of pixel data and when exploded will take something like 40mb or more to process.

Normally this shouldn't be an issue, but the combined memory usage of your install is lilely not leaving much for image processing. For example if you've 100mb or 128mb being used then there's barely any memory available for other processes. You can try using PHP.ini to increase your memory limit to something like 256mb and see if that'll help. You may also want to consider switching to ImageMagick if your host allows it as GD is known for being extremely heavy on memory.

If you need a quick way to judge an images memory size you can use Gimp. Open the image then under Image > Image Properties you'll see in the window that pops up "Size in memory". Just as an example my 1920x1200 image that's 461kbs in size takes up 22mb of memory as raw data.

We've completely replaced our image processing library in CB 2.x. Both the new library and CB it self have a higher memory demand than CB 1.x. So immediately you will already have lower memory available due to this. The new image library is more accurate with its processing and as a result more heavy.

You will need to increase your memory limits or ensure ImageMagick (takes less memory than GD) is properly setup. For ImageMagick it needs to be correctly loaded, its Imagick class available, and it needs to be at least version 6.2.9.