I am guessing you have a stirng that happens to have the \" character in it. This is unnecesary and won't work. Try the following
In[6]:= GenomeData["SCNN1A"]//Short
Out[6]//Short= CCGGCCAGCGGGCGGGCTCCCCAGCCAGGCCGC\[Ellipsis] TAGGCAGGAGCTCAATAAATGTTTGTTGCATGAA
In[3]:= a = "SCNN1A"
Out[3]= SCNN1A
In[4]:= FullForm[a]
Out[4]//FullForm= "SCNN1A"
In[8]:= GenomeData[a]//Short
Out[8]//Short= CCGGCCAGCGGGCGGGCTCCCCAGCCAGGCCGC\[Ellipsis] TAGGCAGGAGCTCAATAAATGTTTGTTGCATGAA
In[5]:= b = "\"SCNN1A\""
Out[5]= "SCNN1A"
In[10]:= FullForm[b]
Out[10]//FullForm= "\"SCNN1A\""
In[9]:= GenomeData[b]//Short
During evaluation of In[9]:= GenomeData::notent: "\"SCNN1A\"" is not a known entity, class, or tag for GenomeData. Use GenomeData[] for a list of entities. >>
Out[9]//Short= GenomeData["SCNN1A"]
You can often identify issues like this with the FullForm function. At any rate, I would suggest not change the single quotes into double quotes, but removing them entirely.
