Error on Tiff and other filetypes

[anonymous]

When uploading certain types of files - as image or normal attachment button - causes the following problem:

Trac detected an internal error:
IOError: decoder group4 not available

Traceback

Python Traceback

Most recent call last:
File "/usr/local/lib/python2.6/site-packages/Trac-0.11.5-py2.6.egg/trac/web/main.py", line 444, in _dispatch_request
File "/usr/local/lib/python2.6/site-packages/Trac-0.11.5-py2.6.egg/trac/web/main.py", line 205, in dispatch
File "/usr/local/lib/python2.6/site-packages/Trac-0.11.5-py2.6.egg/trac/attachment.py", line 398, in process_request
File "/usr/local/lib/python2.6/site-packages/Trac-0.11.5-py2.6.egg/trac/attachment.py", line 612, in _do_save
File "/usr/local/lib/python2.6/site-packages/Trac-0.11.5-py2.6.egg/trac/attachment.py", line 247, in insert
File "/usr/local/lib/python2.6/site-packages/ImageTrac-0.3.1-py2.6.egg/imagetrac/image.py", line 157, in attachment_added
File "/usr/local/lib/python2.6/site-packages/ImageTrac-0.3.1-py2.6.egg/imagetrac/image.py", line 190, in create_sizes
File "/usr/local/lib/python2.6/site-packages/cropresize-0.1.1-py2.6.egg/cropresize/__init__.py", line 46, in crop_resize
File "/usr/local/lib/python2.6/site-packages/PIL/Image.py", line 1256, in resize
File "/usr/local/lib/python2.6/site-packages/PIL/ImageFile.py", line 180, in load
File "/usr/local/lib/python2.6/site-packages/PIL/Image.py", line 375, in _getdecoder

Tried uploading files that previously worked - now returns this error. Also returns error on group3 tif files, .ico files etc.