Unable to evaluate Groovy in Eclipse (GGTS) when debugging

Question

I'm using GGTS for Groovy project and during debug in some cases it's impossible to evaluate the the value of some expressions. The expressions I'm trying to evaluate are simple as a variable value, but when I try it shows an exception like this:

See error log: (Groovy) Complete snippet:
/////start
package adminsite;
import grails.converters.JSON;
import modules.arteplastico.ArticleObraPlasticaTmp;
import modules.arteplastico.dto.ArticleObraPlasticaDTO;
import com.google.gson.JsonObject;
params.accion
/////end

(Groovy) An exception ocurred during evaluation
Evaluation snippet:

Any suggestion?

Edit:

I've find out something more in Eclipse logs:

Caused by: org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
____Eval.groovy: 8: unable to resolve class core.ArticleTmpStatus
 @ line 8, column 13.
 import core.ArticleTmpStatus;
           ^

____Eval.groovy: 5: unable to resolve class modules.arteplastico.dto.ArticleObraPlasticaDTO
 @ line 5, column 33.
   import modules.arteplastico.dto.ArticleObraPlasticaDTO;
                               ^

____Eval.groovy: 9: unable to resolve class core.BaseDTO
 @ line 9, column 13.
   import core.BaseDTO;
           ^

____Eval.groovy: 4: unable to resolve class modules.arteplastico.ArticleObraPlasticaTmp
 @ line 4, column 29.
   import modules.arteplastico.ArticleObraPlasticaTmp;
                           ^

____Eval.groovy: 10: unable to resolve class core.CoreController
 @ line 10, column 13.
   import core.CoreController;
           ^

____Eval.groovy: 11: unable to resolve class core.ModuleIfce
 @ line 11, column 13.
   import core.ModuleIfce;
           ^

____Eval.groovy: 7: unable to resolve class core.ArticleTmp
 @ line 7, column 13.
   import core.ArticleTmp;
           ^

The strange thing is I'm running this code with no problems and at runtime all this classes work properly. The thing is that in Eclipse neither (Ctrl+Space) nor the Debugger are able to find this classes.