Mql5: why can't I convert a string number read from a cvs file to a double

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C++

MQL5 code:
When reading a number stored in a file I cannot convert it to a double
Here is the file contents
3733.31
EURUSD,Sell,0.1,1.07772
I read the first value into a string and then try converting it to a double
It reads the string value but StringToDouble converts it to 0

What I have tried:

int fHandle = FileOpen("TradeSeries.CSV",FILE_READ |FILE_CSV,",");
FileSeek(fHandle,0,SEEK_SET);  //beginning of file
string strEquity = FileReadString(fHandle); //read in equity amt as string
double seriesEquity = StringToDouble(strEquity);   //convert to number
PrintFormat("The string '%s' is converted to the real number %.2f", strEquity, seriesEquity);
//Prints The string 3733.31  is converted to the real number 0.00

//if I place a number in strEquity the conversion works
string strEquity = "3733.31";
double seriesEquity = StringToDouble(strEquity);   //convert to number
PrintFormat("The string '%s' is converted to the real number %.2f", strEquity, seriesEquity);
//Prints The string 3733.31  is converted to the real number 3733.31<pre lang="C++">