Why did VB Break?

[alex21]

My program was working fine a few days ago, I opened my project today to do some more work and i got this error.

Error	1	Overload resolution failed because no accessible 'Format' can be called with these arguments:
    'Public Shared Function Format(provider As System.IFormatProvider, format As String, ParamArray args() As Object) As String': Expression does not produce a value.
    'Public Shared Function Format(provider As System.IFormatProvider, format As String, ParamArray args() As Object) As String': Expression does not produce a value.
    'Public Shared Function Format(provider As System.IFormatProvider, format As String, ParamArray args() As Object) As String': Expression does not produce a value.
    'Public Shared Function Format(provider As System.IFormatProvider, format As String, ParamArray args() As Object) As String': Expression does not produce a value.
    'Public Shared Function Format(provider As System.IFormatProvider, format As String, ParamArray args() As Object) As String': Expression does not produce a value.
    'Public Shared Function Format(format As String, ParamArray args() As Object) As String': Expression does not produce a value.
    'Public Shared Function Format(format As String, ParamArray args() As Object) As String': Expression does not produce a value.
    'Public Shared Function Format(format As String, ParamArray args() As Object) As String': Expression does not produce a value.
    'Public Shared Function Format(format As String, ParamArray args() As Object) As String': Expression does not produce a value.
    'Public Shared Function Format(format As String, ParamArray args() As Object) As String': Expression does not produce a value.	C:\Users\Alex\Documents\My Projects\Stock Assistant\Stock Assistant\frm_Main.vb	959	51	Stock Assistant

From a line of code that worked perfectly a few days ago,

String.Format("INSERT INTO data_sources (data_name, data_websource, data_source_url, data_auto_retrieve, data_retrieval_interval, data_last_retrieve, data_password_required, data_username, data_password) VALUES ('{0}', '{1}', '{2}', '{3}', '{4}', '{5}', '{6}', '{7}', '{8}')", DataManagement.SQLite_SafeString(txt_data_sources_data_name.Text.ToLower()), DataManagement.SQLite_ConvertBoolean(rb_data_sources_websource.Checked), DataManagement.SQLite_SafeString(txt_data_sources_url.Text), DataManagement.SQLite_ConvertBoolean(chk_data_sources_auto_retrieve.Checked), DataManagement.SQLite_SafeString(txt_data_sources_retrieval_interval.Text), DataManagement.SQLite_ConvertDateTime(DateTime.Now), DataManagement.SQLite_ConvertBoolean(DataSources_Current_PasswordRequired), DataManagement.SQLite_SafeString(DataSources_Current_Username), DataManagement.SQLite_SafeString(DataSources_Current_Password))

This error is coming from every String.Format() in one single file of my project, what has happened has my project been corrupted? Why are the other files not throwing this error, why after leaving a working project for a few days am i now faced with a broken project and an error that does not make any sense?

Thanks Alex.

[RedSon]

Is it because you mix ' and "?