New Post: Problem trying to save a workbook

I am having a strange problem when trying to save a particular workbook - the error is:

"Unable to determine the identity of domain."

...and the stacktrace:

at System.IO.IsolatedStorage.IsolatedStorage._GetAccountingInfo(Evidence evidence, Type evidenceType, IsolatedStorageScope fAssmDomApp, Object& oNormalized)
at System.IO.IsolatedStorage.IsolatedStorage.GetAccountingInfo(Evidence evidence, Type evidenceType, IsolatedStorageScope fAssmDomApp, String& typeName, String& instanceName)
at System.IO.IsolatedStorage.IsolatedStorage._InitStore(IsolatedStorageScope scope, Evidence domainEv, Type domainEvidenceType, Evidence assemEv, Type assemblyEvidenceType, Evidence appEv, Type appEvidenceType)
at System.IO.IsolatedStorage.IsolatedStorage.InitStore(IsolatedStorageScope scope, Type domainEvidenceType, Type assemblyEvidenceType)
at System.IO.IsolatedStorage.IsolatedStorageFile.GetStore(IsolatedStorageScope scope, Type domainEvidenceType, Type assemblyEvidenceType)
at MS.Internal.IO.Packaging.PackagingUtilities.ReliableIsolatedStorageFileFolder.GetCurrentStore()
at MS.Internal.IO.Packaging.PackagingUtilities.ReliableIsolatedStorageFileFolder..ctor()
at MS.Internal.IO.Packaging.PackagingUtilities.GetDefaultIsolatedStorageFile()
at MS.Internal.IO.Packaging.PackagingUtilities.CreateUserScopedIsolatedStorageFileStreamWithRandomName(Int32 retryCount, String& fileName)
at MS.Internal.IO.Packaging.SparseMemoryStream.EnsureIsolatedStoreStream()
at MS.Internal.IO.Packaging.SparseMemoryStream.SwitchModeIfNecessary()
at MS.Internal.IO.Packaging.SparseMemoryStream.Write(Byte[] buffer, Int32 offset, Int32 count)
at MS.Internal.IO.Packaging.CompressEmulationStream.Write(Byte[] buffer, Int32 offset, Int32 count)
at MS.Internal.IO.Packaging.CompressStream.Write(Byte[] buffer, Int32 offset, Int32 count)
at MS.Internal.IO.Zip.ProgressiveCrcCalculatingStream.Write(Byte[] buffer, Int32 offset, Int32 count)
at MS.Internal.IO.Zip.ZipIOModeEnforcingStream.Write(Byte[] buffer, Int32 offset, Int32 count)
at System.Xml.XmlUtf8RawTextWriter.FlushBuffer()
at System.Xml.XmlUtf8RawTextWriter.RawText(Char* pSrcBegin, Char* pSrcEnd)
at System.Xml.XmlUtf8RawTextWriter.RawText(String s)
at System.Xml.XmlUtf8RawTextWriter.WriteStartElement(String prefix, String localName, String ns)
at System.Xml.XmlWellFormedWriter.WriteStartElement(String prefix, String localName, String ns)
at DocumentFormat.OpenXml.OpenXmlElement.WriteTo(XmlWriter xmlWriter)
at DocumentFormat.OpenXml.OpenXmlCompositeElement.WriteContentTo(XmlWriter w)
at DocumentFormat.OpenXml.OpenXmlElement.WriteTo(XmlWriter xmlWriter)
at DocumentFormat.OpenXml.OpenXmlCompositeElement.WriteContentTo(XmlWriter w)
at DocumentFormat.OpenXml.OpenXmlElement.WriteTo(XmlWriter xmlWriter)
at DocumentFormat.OpenXml.OpenXmlCompositeElement.WriteContentTo(XmlWriter w)
at DocumentFormat.OpenXml.OpenXmlPartRootElement.WriteTo(XmlWriter xmlWriter)
at DocumentFormat.OpenXml.OpenXmlPartRootElement.SaveToPart(OpenXmlPart openXmlPart)
at DocumentFormat.OpenXml.OpenXmlPartRootElement.Save()
at DocumentFormat.OpenXml.Packaging.OpenXmlPackage.SavePartContent(OpenXmlPart part)
at DocumentFormat.OpenXml.Packaging.OpenXmlPackage.TrySavePartContent(OpenXmlPart part)
at DocumentFormat.OpenXml.Packaging.OpenXmlPackage.SavePartContents()
at DocumentFormat.OpenXml.Packaging.OpenXmlPackage.Dispose(Boolean disposing)
at DocumentFormat.OpenXml.Packaging.OpenXmlPackage.Dispose()
at ClosedXML.Excel.XLWorkbook.CreatePackage(String filePath, SpreadsheetDocumentType spreadsheetDocumentType) in c:\Source\Sainsburys\SainsburysStoreSpace.64bit\CSharp\SainsburysStoreSpace_CSharp\ClosedXML\Excel\XLWorkbook_Save.cs:line 107
at ClosedXML.Excel.XLWorkbook.Save() in c:\Source\Sainsburys\SainsburysStoreSpace.64bit\CSharp\SainsburysStoreSpace_CSharp\ClosedXML\Excel\XLWorkbook.cs:line 417
at SainsburysStoreSpace_CSharp.GondolaExtractNew.SADHelper.SaveSADWorkBook() in c:\Source\Sainsburys\SainsburysStoreSpace.64bit\CSharp\SainsburysStoreSpace_CSharp\GondolaExtractNew\SADHelper.cs:line 75


...also, the resulting excel file is corrupted - I am prompted to repair it on opening.

I have edited/saved other workbooks with ClosedXML, but I cannot fathom what is going on with this.

Any help greatly appreciated