Print string to file, only parts of the string got printed - excel

Question

I've made an application where users write stuff in Excel cells and that info is then printed to a .txt file.
The info is concatenated into a long string before printing it into the file.
The info is not stored in the Excel sheet. Every time you open the sheet, it loads the info from the .txt file into the different cells. If a user changes the content of a cell the info is then printed to the .txt file. Multiple people are working at the same time, changing the cells. Everyone has got their own version of the empty workbook, where the data loads when the workbook is opened. And when someone changes a cell, the data is printed to the .txt file and is then everyone who is working with the application is reading from the file and getting that cell updated with the new info.
Now, someone copied the content of a cell into another cell and hit Enter (which triggers the concatenation process and stores it into the .txt file) What happened was that all the info after the new info didn't get printed. So the last 30000 characters or so just got lost. I'm thinking the user accidentally copied a character with a special meaning like "Stop reading and print to file" or something. But does characters like that exists? Do you have any clue what might have happened?
This is the code that concatenates the string:
Line = ProjectsArray(0) 'Line is the long string that gets printed to the text file
ProjectsArray(ProjectsArrayPosition) = ProjectNumber 'ProjectsArray is string 'Line' but split into the different projects
'ProjectInfo is a specific project split into its different data points. (Every data point belongs to a Excel cell)
'ProjectsArrayPosition is the place in the array where the current Project lives.
'Every data point is joined with a chr(17) in between.
For i = 1 To UBound(ProjectInfo)
ProjectsArray(ProjectsArrayPosition) = ProjectsArray(ProjectsArrayPosition) & Chr(17) & ProjectInfo(i)
Next i
If UBound(ProjectsArray) > 0 Then
For i = 1 To UBound(ProjectsArray)
Line = Line & Chr(18) & ProjectsArray(i) 'Every project is joined with a chr(18) in between
Next i
End If
On Error GoTo NoPath
Open ProjectsFilePath For Output As #1
Print #1, Line
Close #1
On Error GoTo 0
Here's the code that opens the array:
On Error GoTo NoPath
Open ProjectsFilePath For Input As #1
Line Input #1, Line
Close #1
On Error GoTo 0
ProjectsArray = Split(Line, Chr(18))
For i = 1 To UBound(ProjectsArray)
If CInt(Left(ProjectsArray (i), 6)) = ProjectNumber Then
ProjectInfo = Split(ProjectsArray(i), Chr(17))
ProjectsArrayPosition = i
End If
Next i
Select Case ActiveCell.Address
Case "$N$11"
For i = 0 To UBound(ProjectInfo)
If Left(ProjectInfo(i), 1) = "B" then
ProjectInfo(i) = "B" & Sht.Range("N11").Value
End If
Next i
Case "$G$18"
For i = 0 To UBound(ProjectInfo)
If Left(ProjectInfo(i), 1) = "F" then
ProjectInfo(i) = "F" & Sht.Range("G18").Value
End If
Next i
Case "$M$20"
And so on and so on
End Select
The code above is loaded every time you press Enter.
Private Sub Workbook_Activate()
Application.OnKey "~", "EnterPress"
Application.OnKey "{ENTER}", "EnterPress"
End Sub