Do as the dialog says: Delete all VBA-code in all modules and in the spreadsheets. It is probably protected in some way.
SpreadsheetConverter tries to detect which datatype ranges contain. By doing that, we can generate much more efficient and compact code. Try to make sure that ranges only contain numbers or only texts.
If you get this error message, please verify the calculated values. If you see any unexpected NaN, you have to clean up the ranges.
From the Excel documentation of VLOOKUP:
If range_lookup is TRUE, the values in the first column of table_array must be placed in ascending order: …, -2, -1, 0, 1, 2, …, A-Z, FALSE, TRUE; otherwise VLOOKUP may not give the correct value. If range_lookup is FALSE, table_array does not need to be sorted.
Make sure that the range only contain the active part of the lookup table. Do not include the header in the range. Also make sure that the range is ordered otherwise reorder it.
The third argument of HLOOKUP is the column index. If the value of that argument is outside the range 1 and 51, for example 0, SpreadsheetConverter will not calculcate the correct result since you are making a lookup outside the range. This is just a warning.