Hi David. Thanks for your response.
The problem was solved after I closely looked at the tandem.params file I created after upgrading from 4.5.2 to 4.6. I made a silly copy paste error. In the static modifications section I had two decimal points in one of the modification mass specifications. I am not certain how Tandem treated this, but ASAPRatio treated it as multiple modifications to a single residue, in this case it was [.
This was the erroneous modifications line:
<note type="input" label="residue, modification mass">57.021464@C,48.085.047@[,48.085@K</note>
This is the correct modifications line:
<note type="input" label="residue, modification mass">57.021464@C,48.085@[,48.085@K</note>
The Tandem API suggests that it will use the last instance of a modification to the same residue e.g. 48@K,28@K then it will use 28@K and ignore the 48@K. However, in my case the mistake of 48.085.047@[ was apparently treated as multiple modifications to [. Useless anyway because ASAPRatio could not do anything with that. All the output I got was wrong no matter how I specified the modification masses for ASAPRatio. And setting the -S static flag would cause ASAPRation to fail.
Brian