The desired size is in an incorrect format. This typically means it has not been defined as a percentage or a size (e.g. 10% or 5GB).

How to fix 

Use one of the supported formats for desiredSize in your options file.

Problem examples:

{
  "desiredSize": "500"          // Invalid - missing unit
}

{
  "desiredSize": "500"          // Invalid - missing unit
}

Valid formats:

Percentages:

{
  "desiredSize": "25%"
}

Absolute sizes:

{
  "desiredSize": "500MB"       // B, KB, MB, GB, TB supported
}