Some pictures are not working after upload

I have an issue where some pictures are not being generated for thumbnail when the picture is too big.
I have an image field where I upload a picture to on the node page.
In most cases the picture is uploaded fine but in some it uploads the picture (I can find it on the sever) but it do not produce the different sized versions I have set the system to make and on the node edit page it show up as a missing picture (box with red cross).
If I save the node in this version you cannot enter the node through the menu.

If I delete the picture with the error all is working fine.
Some times I can upload the picture again and all is working fine but mostly the error keep repeating.

If I downsize the picture it has no problem.
It only happens for pictures above 4 mb and mostly only to pictures at 5.5 Mb or more (the server limit is set to 20 Mb).

I admit I cannot even be sure this issues is for IMCE but as the error is connected with the making of thumbnails I write here.
I hope someone can either help me or point me in a good direction.

Thank you.