File_column Plugin "Picture invalid image"

I recently built and hosted a rails site on a Windows development
machine and everything was working fine.

The problem started when I moved the site onto a remote Linux server.
Now, whenever someone tries to upload a picture for their profile, they
get this error:

1 error prohibited this user from being saved
There were problems with the following fields:
* Picture invalid image

I searched Google for “Picture invalid image” and found nothing related
to file_column or rails. I know that the pictures that I am testing it
with are indeed valid because they worked when the site was on the
Windows server.

I have RMagick and ImageMagick installed and I am using the file_column
plugin to upload the images. The file_column plugin calls RMagick to
resize images when they are uploaded (this is when the error occurs).

Is anyone familiar with the “Picture invalid image” error or how I can
possibly get this working?