To change the maximum file size limit for uploads you have to do this on several places:

1. Within Quickr: Site Administration → Other Options → Maximum Attachment Size (Default: 50.000 KB)
2. Within the server document: Internet Protocols → HTTP → Maximum size of request content (Default: 10.000 KB)
3. Within the server document: Internet Protocols → Domino Web Engine → Maximum POST data: (Default: 10.000 KB)

Because of the default settings the maximum file size for uploading is limited to 10 MB if you do not change these settings. Set all values to the same values. The only exception is “Maximum size of request content” which should be set to “0” (unlimited).

All values are in KB so if you want to calculate the correct values you should use the factor 1024 (1 MB = 1024 KB).

[Thanks to my collegue Matt Newton]

There is now a more detailed explanation with some additional settings and troubleshooting tips published in the knowledgebase. Please see this technote.