You appear to be using an outdated version of the library as you are parsing directly from the filename (are you grabbing this from nuget??).
In any event, I converted your pasted example data into a .sam file (below) and ran it through the following code. It appears to work without error. Can you confirm the same is true on your end? If your file was corrupted, this would explain why my cut/paste
version worked but yours did not.
Bio.IO.SAM.SAMParser x = new Bio.IO.SAM.SAMParser();
var stream = File.OpenRead(@"test.sam");
var F = x.Parse(stream);
test.sam file contents (no line breaks for non @ lines)
@HD VN:1.0 SO:unsorted
@SQ SN:AY228557_POLDRM LN:9840
@RG ID:Unpaired reads assembled against AY228557 POLDRM SM:XXXX
M03443:9:000000000-AE7WG:1:1118:4103:173092:N:0:80 16 AY228557_POLDRM 1 255 177I1P10I2P16I29M * 0 0 TGTGTAAATTTGACTGTGCTGACATTGTTGCATGGCGCTGTTGCATTGAATGTCTCATTATTACACTTTAGAAGCGCATAACCAGCTGGAAGCACAAGAGGAAGAGGAAGTAGGCTTTCCAGTCACACCTCAGGTGCCTTTAAGAACAATGACTTATAAGGCTGCATTCGATCTCGGCTTCTTTTTAAAAGAAAAGGGGGGACTGGATGGGTTAATTTACTCTAAGAAA 66C9>70A1385@A907;E@A55@CE=0:303)+FFED5D;9FFGFFD98;=C8DC9+?8FDD8CFA3++=C=@+=,FFEC@;5,9EDEE9DE=D>,FFEE9,9D48E8FDACEDEA,,7FBA?FF?=CFF=9GFCEFGFC,CF9AFEF@@@FDGGGFGDCGGF7CD:7CCF<DEC7E9AGGGGGGGGGGGFDDGGGGGFGGGGGGFGFFGGGGGFC<FGGGFGGGGGG