Solution : https://service.sap.com/sap/support/notes/769378 (SAP Service marketplace login required)
Summary :
When importing a project in the LSMW regardless of the SAP release, a runtime error CONVT_NO_NUMBER might occur if the project was exported with LSMW in Basis Release 6.40. This is caused by incorrect version entries in the LSMW "/SAPDMC/LSCVERSN" table of the exporting system. The displayed LSMW version may incorrectly show '3.0' instead of '4.0.0'. To rectify this, import the correction either through a Support Package or by a transport request using the attached VERSTABLE.SAR file. Subsequently, re-export all previously exported projects to prevent follow-on errors.
Key words :
legacy system migration workbench reason, sar file attached, system displays version, previously exported projects, system displays 'lsmw 3, correct version number, convt_no_number runtime error, relevant support package, lsm workbench, previously exported