How does OpenLayers calculate bounding box coordinates?

I'm trying to display a map using OpenLayers through GeoServer's WMS. I'd like to know how OpenLayers calculates the BBOX coordinates to set them properly with js and avoid the posted error response. I haven't this issue with OpenStreetMap and GoogleStreetMap.

This is the JavaScript code I used in my function:

function myfunc(display, url){
    var params = {};
    params.layers = 'Italy';
    params.format = 'image/jpeg';
    params.transparent = true;
    var options = {};
    options.projection='EPSG:900913';
    options.displayProjection="EPSG:4326";
    options.maxExtent= new OpenLayers.Bounds(-20037508.34, 20037508.34,20037508.34,20037508.34);
    options.isBaseLayer = true;
    return new OpenLayers.Layer.WMS(display, url, params, options);
}

This is the request to the geoserver:

http://mydomain:myport/geoserver/gwc/service/wms?LAYERS=Italy&FORMAT=image%2Fpng&TRANSPARENT=true&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&EXCEPTIONS=application%2Fvnd.ogc.se_inimage&S开发者_JS百科RS=EPSG%3A900913&BBOX=1384430.175625,5152466.50375,1384430.87875,5152467.206875&WIDTH=256&HEIGHT=256

This is the response I'm getting from the geoserver:

400: Resolution (0.00274658203125) is not with 5.0% of the closest grid resolution (0.0023326729820109904)

Try adjusting the map's resolution.

I'm no expert on Geoserver, so apologies if this is trivial.

From what I can gather and guess, this is not an OpenLayers problem, but a Geoserver configuration issue.

It seems like you've set up the "Italy" layer as a precompiled tiled layer, is that correct? And it looks like there is a setting somewhere that determines how close the resolution in a request can be to the preset resolutions in the layer. Could you try some other extent? Maybe "zoom out" a bit? So that your request is closer to the layers resolution?