Got this error this afternoon about space:

System.IO.IOException: There is not enough space on the disk.

   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.FileStream.WriteCore(Byte[] buffer, Int32 offset, Int32 count)
   at System.IO.FileStream.Write(Byte[] array, Int32 offset, Int32 count)
   at ICSharpCode.SharpZipLib.Zip.Compression.Streams.DeflaterOutputStream.Deflate()
   at ICSharpCode.SharpZipLib.Zip.ZipOutputStream.Write(Byte[] buffer, Int32 offset, Int32 count)
   at MailClient.Streams.StreamHelper.CopyStream(Stream inputStream, Stream outputStream, Nullable`1 cancellationToken, ProgressReporter reporter)
   at MailClient.Storage.Backup.BackupCompressionTool.AddFile(FileInfo file, String relativePath, CancellationToken token, ProcessedSizeUpdated tracker)
   at DbBackup.FormBackup.Backup(CancellationToken cancellationToken)
   at DbBackup.FormBackup.<mainform_load>b__27_0(Object a, DoWorkEventArgs b)
at System.ComponentModel.BackgroundWorker.OnDoWork(DoWorkEventArgs e)
at System.ComponentModel.BackgroundWorker.WorkerThreadStart(Object argument)
I have plenty room. Must be something else.</mainform_load>

Hi Joe,

eM Client uses a separate directory for its database. 
Please check where is your database stored (Menu > Tools > Settings > General > Storage) and compare it wit a space on that disk. By default the directory is: C:\Users"Your user account"\AppData\Roaming\eM Client.