Hi Tim,
Since you cannot use tables with type x or xstring in conjunction with the read table statement from what i have read you may want to look into converting the type x or xstring into a type c variable and then doing the read statement.
Take a look at this thread here which does a type x conversion to type c Key of internal table contains a component of type X
Or as was mentioned by peter your syntax may be off slightly but wont know till you post a code sample.
Hope this helps,
Geoffery