ASCII import was mostly broken prior to the latest 8.8 beta of MultiCharts.NET. I use a large amount of historical minute data which I import from ASCIIs, and I'm very glad to see that it's mostly fixed.
Assuming that you've got the file format correct (my fields are, as follows: Symbol;Date;Time;Open;High;Low;Close;Volume)- you should start up QuoteManager. I have read experiences of others having problems adding ASCII data for symbols that are pre-existing, so you may want to delete the offending symbols if MultiCharts added them automatically.
Go to Instrument -> Add Symbol -> Manually. Set Data Source: ASCII Mapping; and Symbol, Category, and Exchange as appropriate. Select OK. Highlight the symbol you just added. Right click it, select Import Data, ASCII. Point it to your data source, select OK, and it will read the file into the MultiCharts database. You should then be able to create your chart. It typically takes a few seconds for MultiCharts to read the data from QuoteManager's DB. I have had more success leaving QuoteManager open while running MultiCharts, but your mileage may vary.
I realize that this question was asked months ago, but I hope that it helps you, or someone else in your situation. The documentation on MultiCharts.NET is very sparse, so the more we write that's googleable for future generations, the better
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