Sandbox access lost from one machine but not another

We've been using the sandbox for testing. We use the sandbox from our development machines and a server. Everything was fine until a few weeks ago. We cannot get documents signed using the test server. I know we were able to get documents signed using the test server last December. In the meantime, everything works fine from my development machine. The code for signing has not changed since last July. The line of code where the exception occurs is: PackageId id = client.CreatePackage(packageBuilder.Build()); The error is: Error in BQODocumentSigning.aspx for package ID '' [IP: 10.250.50.100]Could not create a new package. Exception: Object reference not set to an instance of an object. at Silanis.ESL.SDK.Services.PackageService.CreatePackage(Package package) at Silanis.ESL.SDK.EslClient.CreatePackage(DocumentPackage package) at DocumentSigning.DocumentSession.CreateDocuments(Boolean acceptDocuments, DocumentSigner docSigner, List`1 documents) in C:\VS2005Projects\DocumentSigning\DocumentSigning\DocumentSession.cs:line 148 If you've had this problem, and solved it, I'd appreciate the help.