Hello pmerritt,
There are several settings that deal with upload sizes. You may be running into the execute time. Your hosting provider should be able to tell from the logs.
Here are the settings you may want to check out.
memory_limit
This sets the maximum amount of memory in bytes that a script is allowed to allocate.
Default size 5.3 in is “8M”
post_max_size (must be greater than upload_max_filesize)
Sets max size of post data allowed. This setting also affects file upload.
Default size in 5.3 is “128M”
upload_max_filesize
The maximum size of an uploaded file.
max_execution_time
This sets the maximum time in seconds a script is allowed to run before it is terminated by the parser.
Default setting in 5.3 is “30”
Cheers,