The Alglib Numerical Analysis Library has just been updated. For full details of the changes see: http://www.alglib.net/arcnews.php#date_18_01_2013 , but the significant change for routines linking to my spreadsheets is that the sparse solver has been significantly improved and now successfully solves problems that previously failed to converge.
If you already have alglibnet2.dll installed just copy the new version over it. The new version (dated 18/01/2013) is now included in the 3DFrame download: 3DFrame.zip
If you have not yet installed any spreadsheets linking to the C# version of Alglib, see https://newtonexcelbach.wordpress.com/2012/11/16/frame4-now-with-added-alglib/ for detailed instructions on how to do it.