The scout.bmp file header is 41 4C, which is corrupted. We can fix it by changing it to 42 4D.
Then we can translate the symbol with Sigeriontsevsky dictionary.
```FOR GARY-(7,187) FOR MIKE-(5,69)FOR GARY-182,1,171,82,70,184,93,171,182,93,147,147,134,146,146,108,115,93,184,147,134,146,184,177,1,182,128,93,171,145,130,134FOR MIKE-30,60,3,1,18,18FOR GARY-147,134,1,108,88```
At first we thought it was substitution cipher, but we could not decrypt after some cyrptoanalysis work. After observing the pattern for some time, we assumed that it is encrypted with RSA. GARY uses 187 as N and 7 as e, Mike uses 69 as N and 5 as e. Since N is small, we can compute d easily. After that we can decrypt the message, which is the following(Decrypted numbers range from 1 to 26, which can be mapped into alphabets according to the Sigeriontsevsky dictionary. Space is appended by us),
```Gary: GAR? I FORGOT THE END OF THE FLAG BORSCH
Mike: OURALL
Gary: THANK```
We assumed that the flag is BORSCHOURALL, but we got an "invalid flag" answer.  Then we turned it into lowercase and bingo!