Reduce-Reduce error: .. can follow more than one completed rule

Question

I am using Gold Parser v5.2.

I attempting to slightly modify the Object Pascal Engine (by Rob van den Brink) so that it can parse .dpr and .dpk files as well as .pas files.

The garmmar file (named D7Grammar.grm, in the file downloaded from above link) passes Gold's analysis [Project | Analyze the Grammar] (with the modifications below) but fails with 'Project | Create LALR Parse tables'.

Modifications to 'D7Grammar.grm' file:

1. Find definition for 'FloatLiteral' and rewrite it as this:

   FloatLiteral = {Digit} + '.' + {Digit} +
   

2. Find '<UsesClause>' and rewrite it as this:

   <UsesClause> ::= USES <UnitList> ';'
    | SynError
   

3. Add the following rules

   <UnitRef> ::= <RefID> !see http://stackoverflow.com/questions/35871440/
     | <RefID> IN 'StringLiteral'
     | <RefID> IN 'StringLiteral' Comment Start <RefID> Comment End
   
   <UnitList> ::= <UnitList> ',' <UnitRef>
     | <UnitRef>
   

Having done these, when I issue Project | Create LALR Parse tables' in Gold Parser, I get the following error.

')' can follow more than one completed rule. A Reduce-Reduce error is a caused when a grammar allows two or more rules to be reduced at the same time, for the same token. The grammar is ambigious. Please see the documentation for more information.

Further clicking around displays a table showing/hinting that 'FieldDesignator' and 'EnumId' are the culprits --as well as some more information I have no idea what they mean.

I am guessing this new ambiguity was looked over by older versions of Gold (since D7Grammar.grm had no issues then) but brought to surface by the new version.

Trouble is, other than doing trial-error (mostly copy/paste from random ideas or from other peoples suggestions) I am useless with grammar rules.

Hence, goes without saying, help is badly needed to get past this problem.