Created Unassigned: Loading a new workbook fails under mono [9413]

I am unable to do one of the most basic things, open a new workbook under Ubuntu running monodevelop. The following code:
```
XLWorkbook wb = new XLWorkbook("input.xlsx");

```
throws an exception:

```
System.IO.IOException: Operation not valid when package is read-only
at System.IO.Packaging.Package.CheckIsReadOnly () [0x00000] in <filename unknown>:0
at System.IO.Packaging.PackagePart.CreateRelationship (System.Uri targetUri, TargetMode targetMode, System.String relationshipType, System.String id, Boolean loading) [0x00000] in <filename unknown>:0
at System.IO.Packaging.PackagePart.LoadRelationships (System.Collections.Generic.Dictionary`2 relationships, System.IO.Stream stream) [0x00000] in <filename unknown>:0
at System.IO.Packaging.PackagePart.get_Relationships () [0x00000] in <filename unknown>:0
at System.IO.Packaging.PackagePart.GetRelationships () [0x00000] in <filename unknown>:0
at DocumentFormat.OpenXml.Packaging.PackagePartRelationshipPropertyCollection..ctor (System.IO.Packaging.PackagePart packagePart) [0x00000] in <filename unknown>:0
at DocumentFormat.OpenXml.Packaging.OpenXmlPart.Load (DocumentFormat.OpenXml.Packaging.OpenXmlPackage openXmlPackage, DocumentFormat.OpenXml.Packaging.OpenXmlPart parent, System.Uri uriTarget, System.String id, System.Collections.Generic.Dictionary`2 loadedParts) [0x00000] in <filename unknown>:0
at DocumentFormat.OpenXml.Packaging.OpenXmlPartContainer.LoadReferencedPartsAndRelationships (DocumentFormat.OpenXml.Packaging.OpenXmlPackage openXmlPackage, DocumentFormat.OpenXml.Packaging.OpenXmlPart sourcePart, DocumentFormat.OpenXml.Packaging.RelationshipCollection relationshipCollection, System.Collections.Generic.Dictionary`2 loadedParts) [0x00000] in <filename unknown>:0
at DocumentFormat.OpenXml.Packaging.OpenXmlPackage.Load () [0x00000] in <filename unknown>:0
```

The file has all rwx permissions. Is Linux not supported somehow? Am I making some n00b mistake?