I'm able to reproduce as follows:

1) In Options tab of Export wizard:

-- set Delimiter to "." [period]

-- set Decimal Symbol to "." [period]

2) Set "Format" to be "Excel"

3) Click on "Next" button. You will get an error message. The error message is checking Delimiter against Decimal Symbol. However, when "Excel" is chosen as the format, the entire "Data Format" section is removed and Delimiter field is not displayed.

Recommended fix: when format is of type "Excel", only perform field validation for fields that are used by an Excel based export.

I found two input validation problems with the Export Dialog.

1. Choose only one table to export.
    Options tab:
    - Destination: Export to File
    - File: leave it empty
    Result: no validation error message and data was exported to some unknown file

2. Options tab:
    - Destination: Export to File or Preview Export
    - First, choose Format: Delimited Data and make sure Delimiter in Data Format is , (comma)
    - Decimal Symbol: enter , comma
    - Change Format to INSERT Statements or Excel Workbook
    Result: incorrect validation error message that you must specify a decimal symbol different than the data delimiter

Fixed in ADS-12.0.0, ADS-13.0.0, and trunk.