CKFinder uploading problem: image too big, except its not

I saw that others had this problem as well, but the threads were old. When I try to upload certain BMP images, it reports that the file size is too big, even though I can upload bigger images without any problems. Why is this?

Image file is 4.67 MB, dimensions are 2179x2247, 256 colors (7 used). 

CKFinder version 2.2.2, Init response:

<?xml version="1.0" encoding="utf-8"?><Connector resourceType="Images"><Error number="0" /><ConnectorInfo enabled="true" imgWidth="3840" imgHeight="2160" s="" c="" thumbsEnabled="true" uploadCheckImages="false" thumbsUrl="/Content/_thumbs/" thumbsDirectAccess="false" /><ResourceTypes><ResourceType name="Images" url="/Content/images/" maxSize="10485760" allowedExtensions="bmp,gif,jpeg,jpg,png,tif,tiff,svg" deniedExtensions="" hash="cb2fc25198cf816e" hasChildren="true" acl="255" /></ResourceTypes><PluginsInfo /></Connector>