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Base-64 string error

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Re-formatted data in excel sheet to text, there are no Blob or image fields, however, there is still this error

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Dynamics 365 Business Central

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Holly Huffman 6,538 Super User 2025 Season 2 on at

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Good morning, afternoon, or evening depending on your location!

The Base-64 string error in your Excel sheet might occur due to hidden or unexpected data formats, even if there are no Blob or image fields.
Possible Causes:

Hidden Base-64 Encoded Data:

There might be hidden Base-64 encoded strings in the Excel sheet that are not visible in the text format.

These could be remnants of previous operations or embedded objects.

Formatting Issues:

The re-formatting process might not have fully converted all fields to plain text, leaving some data in Base-64 format.

External References:

The sheet might contain links or references to external files that include Base-64 encoded data.

Solutions:

Inspect the Data:

Use Excel's Find and Replace feature to search for patterns like data:image/png;base64 or other Base-64 prefixes.

Check for hidden rows, columns, or sheets that might contain encoded data.

Clear Formatting:

Select all cells and use the Clear Formats option to ensure all data is plain text.

Export and Re-import:

Export the sheet to a CSV file and re-import it into Excel. This process can strip out hidden formatting and embedded objects.

Check for Macros or Scripts:

If the sheet uses VBA macros or scripts, review the code for any operations involving Base-64 encoding.

Use Data Validation:

Apply data validation rules to ensure that only plain text is entered in the relevant fields.

Hope this is helpful :)

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Ramesh Kumar 7,529 Super User 2025 Season 2 on at

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Hidden Characters or Formatting: Even if cells look like text, Excel may include hidden formatting or non-printable characters. Fix: Save the file as CSV UTF-8 (Comma delimited) and open it in a plain text editor (like Notepad++)

Use the "Validate" action in the Configuration Package before applying data. It can point out issues line by line.

Thanks, Ramesh

If this was helpful, please check the "Does this answer your question?" box and mark it as verified.

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Khushbu Rajvi. 20,603 Super User 2025 Season 2 on at

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You're getting the error because Business Central is trying to decode a Base-64 string, but the input contains invalid characters—this usually happens when a field is expected to contain a Blob or Media (which requires proper Base-64 encoding), but you're importing plain or malformed text instead.

Even if your Excel sheet has only text, a field might still be mapped to a binary type, or there may be hidden characters, formatting, or corruption in the data. To fix it, check your import mapping for any Blob or Media fields, clean the Excel data by copying it into Notepad and back to strip hidden formatting, and ensure no fields contain invalid characters for Base-64.

https://learn.microsoft.com/en-us/dotnet/api/system.convert.frombase64string?view=net-9.0

https://learn.microsoft.com/en-us/answers/questions/1088918/invalid-character-in-a-base-64-string-when-using-c

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