string index out of range: -1

[Cableguy]

Thanks to Simon for solving this issue!
The problem seem to have occurred because of an .mcache file had become corrupted possibly because of a full disk or a system shutdown while MinimServer was writing this file, as Simon put it. He told me to delete all such files in the C:\Users\<username>\AppData\Roaming\MinimServer\dat folder and then to restart Minimserver. I did just that and now everything works again. Thanks again Simon for your excellent support!